Denwa is a SIP phone that allows you to communicate using any VoIP Provider. Fast and Simple. Now with VIDEO call support! Basic Features. Audio/Video Call. Call History. Call Transfer. Call Hold. Do Not Disturb. Hands Free. Mute Mic. Advanced Features. Sip 2. 0 (RFC3261) and related RFCs. Audio Codecs: G. 711 aLaw/uLaw, iLBC, GSM, G. 722. 1, g.