... FreePBX, Broadsoft, Cisco call manager etc. VOIP:SIP 2.0 (RFC3261) and correlative RFCs..Full duplex hands-free speaker phone.NAT transverse: support ... (none, basic, MD5), DNS name of server,Peer to Peer/ IP call.SIP support 2 SIP lines or only one IAX2 ... waiting / 3 way talking/ pagingand intercom/pickup/join call/click to dial/call park.Call control features: Flexible dial map, Hot line,empty calling ...