Let's say I want to set up my own dialin server. I don't have a spare PSTN
phone connection. Getting a geographic incoming number is usually
straightforward (Sipgate et al are free). What are the issues with trying
to do this with VOIP? I suppose the problem is I don't actually want V near
any IP. Is there any protocol to having the PSTN-VOIP gateway act as a
modem, rather than a voice sampler? I know there are protocols for fax, but
for modem data?

Is there some way I could get, say, an encapsulated PPP stream over the net?
Are there services that provide this?

Thanks
Theo