... call, full duplex hand-free speaker phone, support SMS Features: Support SIP 2.0 (RFC3261) and correlative ... RFCs Codec:G.711 A/U Law, G.723.1, G.729a/b ... -free can support 96ms, Hand free Speaker Phone Support Voice Gain Setting, VAD, CNG Full ... free speakerphone NAT transverse: support STUN client SIP support SIP domain, SIP authentication (none, basic, MD5), DNS name ...