It's official: Apple and AT&T will allow VoIP calls over the 3G network, presumably using an iPad or an iPhone. We knew the iPad included a microphone and speaker, however the big news regarding VoIP was revealed in the iPhone OS 3.2 SDK (Software Development Kit) released by Apple yesterday.
VoIP (Voice over Internet Protocol) makes it possible to use services like Skype to make voice calls over the Internet. AT&T and Apple have restricted VoIP applications on the iPhone to Wi-Fi in the past. Now developers are free to develop applications with this capability over the 3G cellular network.