A Free SIP-based User Agent (IP Phone) with all the features of a standard business telephone. The intuitive design and familiar layout provides for easy navigation. Already tested with Toshiba, Dell, Compaq/HP, AudioVox PocketPC devices. Features: Line hold, 3 Lines, Redial, Line Transfer, Recent Numbers List, Caller ID (SIP ID), Mute, Touch-tones (DTMF), Push-to-Talk (Optional), CODEC Selection, Call Timer, Silence Threshold, Backspace/Clear/Delete, Microphone & Speaker Levels, G.711/G.723/GSM Codecs included, NAT/Firewall support, Specify NAT IP to be written in SIP messages.