I have ATT. When they released their marketing blitz on this a month or more ago, I called and asked about it. Essentially, they said that they had an agreement now with Cingular and T-mo that allowed you to use their networks with no roaming fees. Anywhere I've been on the east coast, I've always had at least one of the three for coverage so almost always have had a connection.

I'm hoping that when the ATT/Cingular deal goes through, the combined company will keep the cheap unlimited data plan so I can keep paying the $20 that I'm paying now but get unlimited instead of just 8M of data. Guess we'll see what happens...