METHOD AND SYSTEM FOR PROVIDING SERVICES SEAMLESSLY OVER A GEOGRAPHICALLY DEFINED SERVICE AREA FIELD OF THE INVENTION The present invention relates generally to hybrid satellite-terrestrial systems for interactive services. The present invention specifically relates to a method and system for providing services seamlessly over a geographically defined service area. BACKGROUND OF THE INVENTION In general, satellite communication system is implemented to provide a basic communication for various regions of the earth. The satellite communication systems can provide one-way and two-way multimedia services. However, there are locations where the satellite coverage is impeded due to environmental considerations like mountains, buildings, etc. These problems can be avoided or minimized by terrestrial communication systems. Even though, the terrestrial communication systems provide good communication services, it does not provide much wider coverage than the satellite communication systems. With respect to the conventional satellite and terrestrial communication systems, it is very difficult to provide uniformity of services without harmful interference to the services. Therefore, it is desirable to provide a method and system for providing services seamlessly over a geographically defined service area, which overcomes the above-mentioned problems inherent in the existing systems. OBJECT OF THE INVENTION An object of the present invention is to provide a method for providing services seamlessly over a geographically defined service area, which achieves uniformity of services without any harmful interference to the sen/ices from satellite system and complementary terrestrial segments. Another object of the present invention is to provide a method for providing services seamlessly over a geographically defined service area, which enables interactive one-way and two-way services to defined geographical spots. A further object of the present invention is to provide a system for pfoviding services seamlessly over a geographically defined service area, which achieves integration of satellite system and complementary terrestrial segments. SUMMARY OF THE INVENTION According to one aspect, the present invention, which achieves this objective, relates to a method for providing services seamlessly over a geographically defined service area, comprising: representing a total service area (S = Si U S2 U S3 U... Sz) by combining a set of geographical spot beams (Si, S2, S3...Sz) by means of a set union operator (U), where the set of geographical spot beams is defined by a satellite system. The total service area (S) is decomposed into a subset (A) and its complementary subset (A"^). The subset (A) is associated with the geographical locations where the satellite coverage is available whereas the complementary subset (A*^) is associated with the geographical locations where the satellite coverage is unavailable. The services are rendered over the total service area (S) after assigning frequencies from a super set of frequencies {M^j, j = 1,2... (n+m+p)}, by the satellite system. Then, a set of available frequencies from the super set of frequencies {M^j, j = 1,2... (n+m+p)} is assigned to complementary terrestrial segments, such that the services over the complementary subset (A^) are rendered through the complementary terrestrial segments. Such a method provides an integrated satellite-terrestrial system to achieve uniformity of services without any harmful interference to the services from the satellite system and the complementary terrestrial segments. Moreover, the super set of frequencies {% j = 1,2... (n+m+p)} comprises multiple sets of frequencies { Fi, i = 1, 2, ...n }, {fk, k = 1,2...m } and {0|, 1 = 1,2, ...p }. The frequencies assigned for the satellite services from the same set of frequencies are mutually not equal for the adjacent geographical locations. Similarly, the frequencies assigned for the satellite services from the same set of frequencies may or may not be equal for the non-adjacent geographical locations. The satellite services also include one-way multimedia services and two-way multimedia services, where the one-way multimedia services comprise point-to-point services and point-to-muiti point services. Furthermore, the satellite system receives multimedia contents from a service provider through a broadcast satellite system (BSS) feeder hub. The multimedia contents are transmitted from the satellite system to a set of transceiver devices in the geographical spot beams at one or more frequencies from the set of frequencies { Fi, i = 1, 2, ...n }. The multimedia contents and position tracking signals are received from the transceiver devices by the satellite system at one or more frequencies from the set of frequencies {fk, k = 1,2...m }. The multimedia contents are transmitted to the transceiver devices in the geographical spot beams at one or more frequencies from the set of frequencies {0i, I = 1, 2, ...p }, if the multimedia contents is received directly from the MSS hub. In addition, the multimedia contents received from the service provider are transmitted by the complementary terrestrial segments to the transceiver devices in the geographical spot beams at one or more available frequencies from the set of frequencies { Fi, i = 1, 2, ...n }. The multimedia contents from the MSS hub are transmitted by the complementary terrestrial segments to the transceiver devices at one or more available frequencies from the super set of frequencies {% j = 1,2... (n+m+p)}. The multimedia contents and position tracking signals are received from the transceiver devices by the complementary terrestrial segments at one or more available frequencies from the super set of frequencies {M^j, j = 1,2... (n+m+p)}. According to another aspect, the present invention, which achieves this objective, relates to a system for providing services seamlessly over a geographically defined service area, comprising a satellite system in communication with a service provider and a broadcast satellite system (BSS) feeder hub for rendering the services over a total service area (S) after assigning frequencies from a set of frequencies { Fi, i = 1, 2, ...n }. The total service area (S = Si U S2 U S3 U... Sz) is represented by combining a set of geographical spot beams (Si, S2, Sa-.-Sz) defined by the satellite system by means of a set union operator (U). The satellite system is in communication with a mobile satellite service (MSS) hub for rendering services over the total service area (S) after assigning frequencies for uplink from a set of frequencies {fk, k = 1,2...m } and frequencies for downlink from a set of frequencies {0|, I = 1, 2, ...p}. Complementary terrestrial segments are in communication with the service provider and the MSS hub. The complementary terrestrial segments are integratively coupled with the satellite system for decomposing the total service area (S) into two disjoint subsets (A, A'^), the subset (A) is associated with the geographical locations where the satellite coverage is available and its complementary subset (A*^) is associated with the geographical locations where the satellite coverage is unavailable, such that the complementary terrestrial segments render the services over the complementary subset (A'') after one or more available frequencies are assigned from a super set of frequencies {%, j = 1,2... (n+m+p)}. A further understanding of the nature and the advantages of particular embodiments disclosed herein may be realized by reference of the remaining portions of the specification and the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be discussed in greater detail with reference to the accompanying Figures. FIG. 1 shows an overall architecture of a hybrid satellite-terrestrial system, in accordance with an exemplary embodiment of the present invention; FIG. 2 illustrates frequency allocation plan for the hybrid satellite-terrestrial system, in accordance with an exemplary embodiment of the present invention; FIG. 3 illustrates BSS content delivery via satellite, in accordance with an exemplary embodiment of the present invention; FIG. 4 illustrates BSS content delivery via complementary ground segments, in accordance with an exemplary embodiment of the present invention; FIG. 5 illustrates MSS content delivery via the satellite using MSS link sharing with BSS link, in accordance with an exemplary embodiment of the present invention; FIG. 6 illustrates MSS content delivery via the satellite using MSS forward link in a standalone mode, in accordance with an exemplary embodiment of the present invention; FIG. 7 illustrates MSS content delivery via the complementary ground segments using MSS forward link, in accordance with an exemplary embodiment of the present invention; FIG. 8 illustrates MSS return link via the satellite, in accordance with an exemplary embodiment of the present invention; FIG. 9 illustrates an application of one-way data communication from remote terminals to a MSS hub via the satellite, in accordance with an exemplary embodiment of the present invention; FIG. 10 illustrates MSS return link via the complementary ground segments, in accordance with an exemplary embodiment of the present invention; FIG. 11 illustrates a typical example of frequency allocations for the hybrid satellite-terrestrial system, in accordance with an exemplary embodiment of the present invention; and FIG. 12 illustrates a flowchart of a method for providing services seamlessly over a geographically defined service area, in accordance with an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, an overall architecture of a hybrid satellite-terrestrial system is illustrated, in accordance with an exemplary embodiment of the present invention. The satellite-terrestrial system includes a multimedia head end 101 to aggregate the contents from the content providers 201 via multimedia distribution facilities, multimedia Broadcast Satellite System (BSS^ feeder uplink 150 from the BSS feeder hub 103, a geostationary space segment 104, several geographically defined spots of multimedia satellite downlinks exemplified by first satellite downlink spot 105, second satellite downlink spot 115 and third satellite downlink spot 125, terrestrial rebroadcast using the Complementary Ground Segment for BSS content 106 in the first spot 105, Complementary Ground Segment for BSS content 116 in the second spot 115, Complementary Ground Segment for BSS content 126 in the third spot 125, Complementary Ground Segment for additional content 107 for first spot 105, Complementary Ground Segment for additional content 117 for second spot 115, Complementary Ground Segment for additional content 127 for third spot 125, an integrated transceiver device 108 in first spot 105, an integrated transceiver device 118 in second spot 115, and an integrated transceiver device 128 in third spot 125, Mobile Satellite Service (MSS) return uplink 109 to the satellite from the integrated transceiver device 108 in first satellite downlink spot 105, MSS return uplink 119 to the satellite from the integrated transceiver device 118 in second satellite downlink spot 115, MSS return uplink to the satellite from the integrated transceiver device 128 in third satellite downlink spot 125, the MSS return downlink 160 from the satellite to MSS hub 110, a complementary MSS ground segment 111 in first spot 105, a complementary MSS ground segment 121 in second spot 115, a complementary MSS ground segment 131 in third spot 125, an additional path for the MSS forward link 112 to the integrated transceiver device 108 in first satellite downlink spot 105 from the space segment 104, an additional path for the MSS forward link 122 to the integrated transceiver device 118 in the second satellite downlink spot 115 from the space segment 104, an additional path for the MSS foHA/ard link 132 to the integrated transceiver device 128 in the third satellite downlink spot 125 from the space segment 104, the two-way link 160 between the space segment 104 and the MSS hub 110, and two-way links for the MSS hub 110 to the public networks exemplified by PSTN 202, GSM network 203 and the Internet 204. The multiplicity of services from the integrated satellite-terrestrial system of FIG. 1 is delivered by assigning frequencies and bandwidths appropriate to enable the services. FIG. 2 illustrates a frequency allocation plan for the hybrid satellite-terrestrial system, in accordance with an exemplary embodiment of the present invention. The frequency allocation plan is defined as three bands of frequencies, i.e. MSS downlink, BSS downlink and MSS uplink. The downlink and uplink convention is from the perspective of the satellite system. Each of these bands comprises one or more sets of assignable frequencies which are allocated among the satellite segment for MSS downlink, BSS downlink and MSS uplink, and for the transmit and receive for the Complementary Ground Segment for delivering the services. The allocation is made such that the services are provided seamlessly over a defined service area. The geostationary satellite system 104 supports a plurality of services, with one of the services involving subsystems 101, 103, 104, 105, 106 and 107 for broadcasting multimedia contents to transceiver systems exemplified by 108, 118 and 128 in the geographically defined spots exemplified by 105, 115 and 125, respectively, and at least another service involving subsystems 109, 104, 160,110, 103, 150 and 105 for two-way communications involving \he transceiver systems exemplified by transceiver device 108 in the first spot, and similarly in the other spots. Thus, the hybrid satellite-terrestrial system provides one-way multimedia services and two-way multimedia services, where the one-way multimedia services include point-to-point services and point-to-muiti point sen/ices. The services from the satellite system share one or more satellite uplink beams, satellite downlink beams or combinations thereof. The two or more satellite services are co-located and combined to produce the services not possible to be provided by any one of the two or more satellite services individually. Such integrated satellite-terrestrial system employs transmission protocols including Internet Protocol v4, v6, and encoding schemes including MPEG2 and MPEG4, and modulation schemes including OFDM, BPSK, QPSK and QAM. The geostationary satellite system 104 transmits multimedia satellite downlink at one or more assigned frequencies from the set (Fi) using an assigned bandwidth of BWi, per geographically defined spot beam where i can be chosen from {1, 2, ...n}. Each geographically defined spots has a given assignment of the frequency set, for example, frequency (Fji) and bandwidth BWii for the first satellite downlink spot 105, frequency (Fj2) and bandwidth BWi2 for the second satellite downlink spot 115, frequency (Fjs) and bandwidth BWis for the third satellite downlink spot 125 and so on. The bandwidths associated with the different spots, namely, BWn, BW12, B\N\z may or may not be equal. If SI, S2, S3... denote the set of all geographical locations that belong to first, second, third... spot beams, respectively, the total service area is defined by S = SI U S2 U S3 U..., where U is the set Union operator. In particular, the total service area (S) is represented by combining the geographical locations (S1, S2, S3..,Sz) defined by the satellite system 104 using the set union operator (U). The total service area S can further be decomposed in terms of the collectively exhaustive, disjoint subsets A and A*^, where A is the set of all geographical points where there is direct satellite coverage, and A"^ is the complement of the set A, which represents the geographical locations where the satellite signal is disadvantaged by factors such as blockage and interference. The proposed integrated satellite-terrestrial system offers the services over the entire set S and hence for those locations that belong to A*^, the services are rendered by the Complementary Ground Segment by using a proper assignment of frequencies from the universal set of available frequencies, namely {'+'j, j = 1,2... (n+m+p)} that includes the three sets, namely, [{ Fi }, where i can be (1, 2, ...n)], [{fk }, where k can be (1,2...m)], and [{cpl}where I can be (1,2,..p)], such that the assignment to the Complementary Ground Segment is made in a way that it does not cause harmful interference to the services from the satellite for the spot Si in which the geographical location falls. The satellite system 104 is in communication with the service provider 201 and the BSS feeder hub 103 for rendering the services over the total service area (S) after assigning one or more frequencies from the set of frequencies { Fi, i = 1, 2, ...n }. The satellite system 104 in communication with the mobile satellite service (MSS) hub 110 for rendering services over the total service area (S) after assigning one or more frequencies for uplink from the set of frequencies {fk, k = 1,2...m } and one or more frequencies for downlink from the set of frequencies {Oi, I = 1, 2, ...p}. Similarly, the complementary terrestrial segments 106, 107, 111, 116, 117, 121, 126, 127, 131 are in communication with the service provider 201 and the MSS hub 110. The complementary terrestrial segments 106, 107, 111, 116, 117, 121, 126, 127, 131 are integratively coupled with the satellite system 104 for decomposing the total service area (S) into two disjoint subsets (A, A*^), such that the complementary terrestrial segments 106, 107, 111, 116, 117, 121, 126, 127, 131 render the services over the complementary subset (A"^) after one or more available frequencies are assigned from the super set of frequencies {M^j, j = 1,2... (n+m+p)}. « If the geographically defined first satellite downlink spot 105 and the second spot 115 are adjacent, the assignments of the frequency sets for the multimedia satellite downlink for the spots are mutually exclusive, namely i1 ^ i2, where both Hand 12 are chosen from {1, 2, ...n}. If the geographically defined first satellite downlink spot 105 and the third spot 125 are non-adjacent, the assignments of the frequency sets for the multimedia satellite downlink for the spots have no restrictions, with both i1 and 13 chosen from {1, 2, ...n}, including the possibility of the frequency reuse from the satellite, namely i1 = 13. For the geographically defined first satellite downlink spot 105, the terrestrial transmissions of the satellite multimedia content may or may not reuse the satellite downlink frequency set (Fji) nor its bandwidth BWn, whereas additional terrestrial multimedia transmissions to the transceiver device 108 use the frequency set (Fji)^, where (Fji)^ is the complement of the frequency set (Fji), complemented over the entire band of assignable satellite downlink frequencies [Fj^, i1 belonging to {1, 2, ...n}]. MSS forward link could use for its downlink either the BSS assignment of (Fji) for the first satellite downlink spot 105, (Fj2) for the second satellite downlink spot 115, (Fjs) for the third satellite downlink spot 125, or alternatively the MSS-specific frequencies from the set 0| where I can be {1,2,..o}. MSS return link could use for the uplink frequency f^ where k can be {1,2...m}. The duplex scheme may be Time Division Duplex (TDD) or Frequency Division Duplex (FDD) and in the case of FDD, the frequencies assigned for the forward and return links may or may not be paired. Multimedia Head End 101: The multimedia head end 101 of satellite-terrestrial system accepts the audio, video and data contents from diverse sources, in diverse formats and from diverse media. The multimedia contents may include, but is not limited to one or more of voice, text, audio, still images, animation, video, and rich media content forms. The head end includes antennas, receivers, signal processing units, protocol converters, formatters, incorporation of Forward Error Correction, coders, modulators. Digital Rights Management systems and the like, in order to output the broadcast contents as an Internet Protocol (IP) stream. The multimedia distribution facilities comprise a minimum of two components, one for interfacing with the satellite uplink station and the other for backhauling the contents to the terrestrial transmitting network 106 and 107 in the geographically defined first spot, 116 and 117 in the second spot, 126 and 127 in the third spot and so on. Depending on the geographical location of these satellite and terrestrial stations, the distribution facilities may include of C, extended C or Ku band satellite links, line-of-sight microwave links or leased IP circuits or VPN links. BSS Feeder Hub 103: The BSS feeder hub 103 provides multimedia satellite feeder uplink 150 and includes the baseband system, up converters, RF amplifiers and antennas. The feeder link uses the frequencies from a set of frequencies { F,', i=1, 2, ...n }, where the downlink frequency f\ of the geographically-defined spots correspond to the feeder link frequency f\ and the feeder links operate in a single beam whose coverage is the set Union S of the coverage of the entire set of spot beams. Space Segment 104: The geostationary satellite system 104 may be located over the equator at such a height that its period of revolution matches with the period of Earth's rotation over its axis. Also the longitude over which the satellite is maintained is such that the satellite is radio-visible over the sen/ice region of interest. The space segment considered herein includes one or more co-located or non-co-located geostationary satellites and delivers plurality of services that include but not limited to Broadcast Satellite Service (BSS) and Mobile Satellite Service (MSS). One of the satellite payloads is for Broadcast Satellite Service (BSS) and has the capability to receive the multimedia content transmitted from the uplink facility described as 103 in FIG. 1, frequency translate as appropriate, power amplify the signal and transmit it over the assigned downlink spot beam. The BSS utilizes specific frequencies allocated by regulatory bodies at specific orbital locations for domestic or regional service. BSS provides a broadcast of audio or video or data or any combination thereof to devices located in the service region of the satellite. The contents are uplinked from a single or multiple hubs. The BSS service region considered herein includes a plurality of geographically defined spot beams. Within each spot the contents that are broadcast are identical. The broadcast contents in different spot beams could be different or same or partially common. The multiple spot beams collectively serve the service region. The downlink frequency and bandwidth for each of the spot beams are assigned on the basis of a frequency allocation plan. The Mobile Satellite Service (MSS) is characterized by a return link, from the device to a ground-based MSS hub 110, and a forward link, from the MSS hub 110 to the device. MSS payload has the capability to receive transmission from a device described as 108 or 118 or 128 in FIG. 1 as well as be able to transmit content transmission addressed to a specific device as shown by the links 112,122 and 132 in the three spots depicted in FIG. 1. Geographical Spot Beams 105, 115 and 125: The geographically defined spots of multimedia satellite downlinks exemplified by 105, 115 and 125 refer to a contiguous area on the surface of the Earth where the satellite downlink signal is concentrated in power by using a high gain antenna on the satellite. Each spot beam covers a limited geographic area on Earth that may remain fixed during the lifetime of the satellite or may be altered depending on the mission requirements. Complementary Ground Segment for Multimedia Services: in order to extend the service into dense urban conglomerates where the satellite signal could be too weak or prone to interference, the multimedia contents as corresponding to that geographical location as decided by the satellite spot beam, may be terrestrially transmitted using the BSS downlink band of frequencies. These terrestrial transmitters receive the multimedia contents either from the satellite or through a backhaul terrestrial link, amplify the signals and retransmit at the satellite downlink frequency or at another frequericy from within the set of assigned frequencies for the BSS service from the space segment to allow penetration into buildings, foliage etc. The terrestrially transmitted multimedia download may be a superset of the satellite content with the inclusion of additional regional and local contents. The Complementary Ground Segment may be dedicated to this mission or could be integrated onto an existing ground system or network. Complementary Ground Segment for BSS Contents 106, 116 and 126: The terrestrial rebroadcast of the satellite, exemplified by Complementary Ground Segment for BSS content 106 in the first spot 105, Complementary Ground Segment for BSS content 116 in the second spot 115, Complementary Ground Segment for BSS content 126 in the third spot 125, includes receiving the satellite uplink content from the multimedia head end 101 via the multimedia distribution facilities. In embodiments in which a Single Frequency Network (SFN) is adopted, it is properly time synchronized with the satellite downlink signal so that the given device for example in the first spot would receive the same content from the terrestrial rebroadcast Complementary Ground Segment for BSS content 106 in the first spot 105 or from the satellite downlink to spot 105 seamlessly, depending on the selection criterion incorporated in the device for selecting between the satellite and terrestrial signals. However, the satellite-terrestnal system is capable of supporting both synchronous and non-synchronous modes of delivery of multimedia contents to devices. The Complementary Ground Segment subsystem 106, 116 or 126 comprises antennas, transceivers, reformatters and inter facility links. Complementary Ground Segment for Additional Content 107, 117 and 127: The supplementary terrestrial transmission exemplified by Complementary Ground Segment for additional content 107 for first spot 105, Complementary Ground Segment for additional content 117 for second spot 115, Complementary Ground Segment for additional content 127 for third spot 125 includes additional content from the multimedia head end 101 via multimedia distribution facilities for terrestrial distribution. The subsystem comprises antennas, transceivers, reformatters and inter-facility links. 15 Transceiver Devices 108, 118 and 128: The transceiver systems as embodied in transceiver devices 108, 118 and 128 may comprise antennas for receiving the satellite and/or terrestrial transmissions, low noise amplifiers, filters, tuners, signal processors, decoders and appropriate output interfaces for the content. The device may be dedicated to one or more services offered by the space segment 104, or may be incorporating in an existing device for other purposes, the use with the space segment 104. It could have a variety of form factors and shapes. Also, the device may be modular in terms of working with the terrestrial components of the services offered by the integrated satellite-terrestrial system, with an optional plug in whenever it has to take advantage of the satellite component of the integrated satellite-terrestrial system. Furthermore, the device may also limit itself to providing access to other commercially available units for the services offered by the integrated satellite-terrestrial system, acting as a gateway. MSS Return Uplinl< 109, 119 and 129: The MSS return uplinks 109, 119 and 129 to the satellite from the integrated transceiver system comprises vocoders, video codecs, data interfaces, signal processors, modulators, amplifiers, antenna to transmit the signal to the geostationary satellite system 104. MSS Hub 110: The MSS hub 110 acts as the gateway for the MSS traffic in both directions. It receives the MSS return link from the satellite and appropriately interfaces it to the outside systems like the PSTN 202 or GSM networks 203. or Internet 204. For the MSS fonward link the MSS hub 110 may receive the data from Internet 204 / PSTN 202 / GSM networks 203 and delivers to the BSS hub 103 for inclusion in the BSS feeder link 150. Alternatively, MSS hub 110 may transmit the forward link directly on its uplink 160 so that the space segment can deliver the content to the intended device 108 or 118 or 128, via the downlink 112 or 122 or 132, respectively. The flexibility in the assignment of frequencies would cater to symmetric or asymmetric allotment of bandwidths for the forward and return links to meet the specific traffic demands from the user perspective. The MSS hub 110 comprises trans-receive antennas, up and down converters, amplifiers and format converters. Complementary Ground Segment for MSS services 111,121 and 131: The MSS Service is further extended by the use of a complementary ground segment by incorporating a network of transceivers with a geographically defined coverage. The cell of coverage for any one of these terrestrial stations is much smaller than the satellite coverage for the forward or return links. These terrestrial stations reuse the satellite frequency band so that the device could transmit to or receive from the satellite or the terrestrial station seamlessly. However, the air interface for the satellite link and the terrestrial link for the MSS service could be same or different. The Complementary Ground Segment may be dedicated to this mission or could be integrated onto an existing ground system or network. The Complementary Ground Segment may use for the forward as well as return links from the super set of frequencies {M-'i, j = 1,2... (n+m+p)} that includes the three sets, namely,[{ Fj}, where i can be (1, 2, ...n)], [{f|^}, where k can be (1,2...m)], and [{