A source IP telephone inputs, from its numeric keypad, a telephone number of a call destination and obtains, from an ENUM server, a NAPTR record of the destination IP telephone based upon the input telephone number of the call destination. By referring to a search table, the source IP telephone retrieves, from the obtained NAPTR record, an available specific number in the ascending order of call rates from the lowest based upon communication services available to the source IP telephone. The source IP telephone transmits a call to the destination IP telephone by using the retrieved specific number.