CEO Steve Jobs says Apple will not block third-party development of VOIP applications for the iPhone and iPod Touch, as long as the applications run over Wi-Fi. That's an obviously politically astute move given Apple's relationship with mobile providers who aren't keen on the idea.
Nevertheless, the idea might allow everybody to get a bit more experience with "dual mode" service, using a widely-deployed handset, without a lot of expensive bets on particular devices, interfaces or marketing.