Features: 1) PnP USB interface, compatible with USB1.1 2) Clear voice quality 3) Built-in DTMF dialing 4) Incoming call ring, easy for answering 5) No sound card and extra power supply required 6) Compact appearance design suitable for notebook 7) Applicable for wide and compatible multi-calling platforms 8) Choosing proper platform to communicate between 2 USB IP phones, it can realize conversation free of charge