1,2 line SIP phone 2,Support 2 SIP Aaccount 3, Support Transfer calls function/Three-way ... then press "CONF" key... 1,Protocol support: SIP(RFC2543,RFC3261);2,Display and store 64 groups of incoming calls;3,Display ... and store 64 groups of outgoing calls;4,Phone Book with 140 groups memory5,Hand-free dialing functions, ... a semiduplex way to ensure the talking quality; Two Line VoIP Phone