I recently got a new phone and I sacrificed US coverage for global
coverage. Occasionally I find my self walking out of a forest in some
1st-2nd-3rd world nation and need to find transportation and/or food.
I got the AT&T GSM plan with a quad-band NEC phone and it works great.
I was initially concerned about US coverage but then it occured to me
that my US travels are either all metro where any mobile phone works,
or BFE where no mobile works. So in my case a smaller US GSM coverage
doesn't hurt very much.

-lance smith