Gizmodo's Brian Lam (no, not the C-SPAN guy, that'd be Brian Lamb) notes a snippet from Apple's SDK-coming-out-part press conference in which one Mr. Jobs noted that any third-party iPhone developer cooks up a VoIP program for iPhone, the utility will be allowed to work via any Wi-Fi hotspots that might be in range.
VoIP over iPhone via AT&T' Mobility's cell network. Sorry, not gonna happen.
Brian thinks VoIP over iPhone WiFi is going to be "huge."
I'm not so sure, though. Mobile VoIP is making some inroads in the enterprise and SMB sectors, but less so for the consumer. I mean, Vonage tried VoIP over Wi-Fi, but then quietly dropped their offering. Not enough demand, and reports of less-than-stellar tech quality.
Before I offer more a more conclusive assessment about the longer-term prospects VoIP over iPhone, let me see what the 3P devs come up with.