You can answer it for incoming calls like a normal office voip phone, without the need to worry about limited battery life or paying for a live SIM card just to have a toy to play around with. For people who already have their own SIP based IP PBX the cost of adding another phone is zero.

For outbound calls if you encounter an IVR menu (press 1 for english, etc), the ATA will translate pulse dialing into DTMF tones. Functionality I think this example is lacking.