Doesn't work. Just tried to swap my iPad and iPhone 4 SIMs. Both devices noticed the switch and showed the phone numbers (yep, the iPad has a phone number), but both complained they weren't set up for a data plan. Even after a restart, neither device allowed me to set the APN. I do know that the iPad on AT&T uses a different APN setting then the iPhone and other smartphones, so that probably has something to do with it. I could probably override this with a configuration profile, but at that point it starts to get annoying.