1) Call is not billed (when staying on VOIPo's network).

2) A SIP address usage example, would be as follows:

John Smith has phone number "9496805673" under his reseller account.

John sets Incoming calls to this phone number to forward to: sip:SomeSipURI@someHost.com as the "destination".

The incoming leg (call TO 9496805673 would be billed at whatever applicable rate, and then the outbound forwarding leg would be free, because it is a SIP address / URI ).

Let me know if this clears the air, thanks!