[j_b_f]

Sure, I get that. But the description above should suffice for most people. It's the same terminology used by the GSM Association: http://www.gsmworld.com/roaming/gsminfo/index.shtml (this link is awesome in that it shows you what bands the different carriers use for various services)

[cliff]

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.

[j_b_f]

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.