It supports voice and fax. Suppose you try to call somebody and they are on a call. Q.sig allows you to dial a code and hang up, and when their call completes your telephone rings. When you pick it up their telephone rings and you are thus connected to them. VoIP gives you this ability end to end.
Billing is really easy.
The system currently handles thousands of calls per day. The 47th meeting of the Internet Engineering Task Force is occuring in Adelaide from 26 until 31 March. The meeting collected togeth the people that have built the Internet. Some attendees at the meeting have graciously offered to give one hour free presentations to computer scientists, students and the public.