Telephone applicable to PSTN and IP network and call connection control method

1. A telephone applicable to a public switched telephone network (PSTN) and an Internet Protocol (IP) network, comprising:

a first interface for transmitting and receiving analog signals over the PSTN;

a second interface for transmitting and receiving packet data over the IP network;

means for communicating with a telephone number translation server connected to the IP network through said second interface when a call is originated by entering a PSTN telephone number and obtaining from the telephone number translation server an IP network telephone number of a destination telephone corresponding to the PSTN telephone number;

means for communicating with a call agent connected to the IP network through said second interface to obtain IP address information of the destination telephone corresponding to said IP network telephone number, and establishing a call connection with the destination telephone via the IP network by using the IP address information; and

means for establishing a call connection with the destination telephone via the PSTN through said first interface if the IP network telephone number of the destination telephone corresponding to said PSTN telephone number cannot be obtained from said telephone number translation server.

2. The telephone according to claim 1 , further comprising means for communicating with said telephone number translation server and registering a mapping of the telephone's own PSTN telephone number and IP network telephone number to the server when the telephone is connected to the IP network.

3. The telephone according to claim 1 , wherein, if the entered PSTN telephone number comprises entirely of local exchange code and subscriber number, said means for obtaining the IP network telephone number converts the entered PSTN telephone number into a numbering format including a toll number prior to obtaining the IP network telephone number of the destination telephone.

4. A call connection control method for connecting a calling telephone, which is connected to a public switched telephone network (PSTN) and an Internet Protocol (IP) network, to a destination telephone, comprising the steps of:

communicating with a telephone number translation server connected to the IP network when a call is originated by entering a PSTN telephone number and obtaining from the telephone number translation server an IP network telephone number of the destination telephone corresponding to said PSTN telephone number;

obtaining IP address information of the destination telephone corresponding to said IP network telephone number from a call agent connected to said IP network and establishing a call connection between the calling telephone and the destination telephone via the IP network by using the IP address information; and

establishing a call connection between the calling telephone and the destination telephone via the PSTN if the IP network telephone number of the destination telephone corresponding to said PSTN telephone number cannot be obtained from said telephone number translation server.

5. The call connection control method according to claim 4 , further comprising the step of storing a mapping between the IP network telephone number obtained from said telephone number translation server and said PSTN telephone number into a cache table,

wherein when a call is originated by entering a PSTN telephone number, said cache table is searched for the IP network telephone number of the destination telephone corresponding to the entered PSTN telephone number, and if the IP network telephone number of the destination telephone exists in the cache table, the IP network telephone number is used, and if the IP network telephone number of the destination telephone does not exist in the cache table, the IP network telephone number of the destination telephone is obtained from said telephone number translation server.