Remember this Nokia, Palm and Sony Ericsson pretty much everyone else that produces Cellular phones are producing their next generation phones with WiFi support, just look at the Nokia E61 and Sony Ericsson P990i. They have WiFi and VoIP clients built in, hell the Telco '3' actually has signed a deal with Skype to ship phones with a Skype client built in.

Well, the iPhone has WiFi too. The difference is that those other two phones are not tied to a carrier—the iPhone is tied to Cingular and relies on carrier support for some features (e.g. visual voice-mail), which means that Cingular gets a certain amount of say in what the iPhone can and can't do. My guess, derived from Dan Moren's statement, is that no SDK is one of the terms of Apple's agreement with Cingular.

Basically most of the design features of the iPhone are as a result of the backward thinking of a single US telco, the exclusion of 3G is one example, every telco outside of the US is moving away from providing data services over EDGE and GPRS. It costs them too much in license fees to Nokia and Ericsson. Actually restricting the device in such a way will hurt Apple, as the market for a GSM based phone bigger outside of the USA, and if they are to compete with Nokia and Sony Ericsson and the other established phone providers outside the US they will need to provide more.