In a Q&A session at the end of the SDK Roadmap event, Apple confirmed that while they would not be unlocking the iPhone nor permitting apps that attempted to remove the AT&T SIM lock, VoIP applications that use WiFi (though not EDGE) would be allowed.

“We will only stop VOIP over cell networks, but not WiFi” Steve Jobs, CEO, Apple

The confirmation is being viewed by some as a partial admission from Apple that they recognise many iPhone owners are dissatisfied with the company’s choice of network.

A project to introduce a VoIP client onto the iPhone has already been underway for some time - see http://touchmods.net/ - but the SDK’s access to the WiFi stack and the full media capabilities of the handset should make the task much easier.  Personally, I’m hoping to see Skype on the iPhone.