I’m not so sure that the iPhone will ever support 3G. Methinks, in his heart of hearts, Steve Jobs plans to leapfrog all of that…long-term, the iPhone will essentially be a wireless internet device that can make what amounts to a radio-call in a pinch. Check out this excerpt from an interview with Jobs and AT&T CEO and Chairman Randall Stephenson:

[Stephenson:] Wi-Fi is just an enhancement to your existing wireless capability. I have this perspective that the more wireless we become, the more wireline we become. The deeper you push these wireless capabilities the more you’re relying on the underlying wired transport which is a much faster, high-capacity transport.

AT&T would be insane not to see it this way. Essentially-universal broadband is coming sooner or later. They’re a copper-wire company that needs to be an over-the-air company. If they don’t leverage that existing (and unique) backbone into something useful for a WiFi world they’re out of business; they’re certainly not going to require all that wire for the future’s phone calls. So they gradually morph into a WiFi-providing, fat datapipe company, leveraging a wireless phone userbase that need not even notice the change as it happens. Ultimately, you’re paying a subscription fee to AT&T for WiFi access that happens to include access to EDGE (and 3G) networks for use in a pinch, otherwise known as “away from the city.”
For AT&T it’s a return to the good old days: they control the underlying network, they control the access devices (instead of a Princess Slimline, you get an iPhone or derivative), they subcontract access out to other providers. There is no Step Two. Step three: Profit!