Is It Possible to Receive Incoming Calls on a Virtual # on the iPhone via VoIP. Not Going Through Any PSTN?

When i receive a call to my toll free or any other virtual phone number i want it to be connected to my iphone via VoIP with a fixed number. right now i use VoIP for outgoing calls with fring skype and a SIP provider. I love the cheap rates but the incoming calls don't get transfered to phone. So i was wondering if i can just receive calls with another number in my area code or toll free and have it forward to my accounts. Any feedback on this would be great. If anyone has done anything like this before i would like to hear it.