A telephone switching system includes a position information management database and a call conversion controller. On receiving number conversion information from an adapter having a radio communication terminal connected, the database registers an identification number assigned to the adapter and terminal information particular to the communication terminal in one-to-one correspondence, thereby managing the position of the communication terminal. When a call is originated on a telephone terminal interconnected thereto or a communication terminal having a voice communication function interconnected to its LAN system, the call conversion controller searches the database on the basis of a destination number and substitutes, if terminal information corresponding to the destination number is found out in the database, the identification number of the adapter corresponding to the terminal information for the destination number to process call switching.