US Patent 7653049 IP telephone system, IP telephone apparatus and calling method

An IP telephone system includes IP telephone apparatuses and an ENUM server. The IP telephone apparatuses, connected to an IP network, perform a voice communication. The ENUM server stores NAPTR resource records containing file transfer protocols supported by the IP telephone apparatuses and returns the NAPTR resource records, responding to a query of the IP telephone apparatuses. In the IP telephone system, when receiving a voice communication instruction from a user of a source IP telephone apparatus the source IP telephone apparatus inquires the ENUM server for NAPTR resource records of a destination IP telephone apparatus. When receiving a file transfer instruction during a voice communication, the source IP telephone apparatus transfers a file to the destination IP telephone apparatus, using a file transfer protocol specified in the NAPTR resource records.