The description might be sufficient, but it's inaccurate. You can't say AT&T 850/1900 and T-Mo 1700/2100 in one sentence. It's not the same context. You can say AT&T 850/1900 and T-Mo 1700.
The point is it's more difficult for phone manufacturers to make world phones for AT&T because they have to use up two bands just for AT&T, and those two bands are not commonly used in Europe or Asia.
Okay, yeah, you're right. But the takeaway is that while the two American networks are incompatible both the N1 and the iPhone should support world roaming equally well.
The point is it's more difficult for phone manufacturers to make world phones for AT&T because they have to use up two bands just for AT&T, and those two bands are not commonly used in Europe or Asia.