Will the AT&T iPhone data plan restrict you to just the iPhone?

After reading that there will be specific data plans for the iPhone I am more hesitant to make the switch and go for this latest gadget. While I would expect to use the iPhone as my main device after shelling out a few bucks for the iPhone, I also want the flexibility to pop my SIM out and put it into an AT&T or unlocked Nokia or Windows Mobile smartphone when the iPhone battery dies or I find I really do want buttons on my phone.

After reading that there will be specific data plans for the iPhone I am more hesitant to make the switch and go for this latest gadget. While I would expect to use the iPhone as my main device after shelling out a few bucks for the iPhone, I also want the flexibility to pop my SIM out and put it into an AT&T or unlocked Nokia or Windows Mobile smartphone when the iPhone battery dies or I find I really do want buttons on my phone. The particular section from the article that has me a bit concerned is:

There are other surprises in the works for June 29. In addition to launching the iPhone that day, Carter says AT&T also will announce new service plans for it.He declined to be specific, but says plans will be customized for the iPhone.

I was hoping they would just use their PDA or Smartphone data plan with a special pricing for iPhone buyers. It remains to be seen what limitations, if any, there will be on the data cross-platform functionality though as this and several other questions will be unanswered until at least 29 June.