The cell sites the phone picks up is determined by the PRL(roaming list) on the handset. It is a local service, therefore when you are out of the "local" area, even if you want to make a credit card call, you will not be able to. Because the phone does not see a site that will accept it's call.

I don't know how much you travel out of your local area. But your best bet is to put something like Alltel pre-pay on NAM2, and your Metro service stays on NAM1. When you travel, just switch to NAM2 and you will have service outside of that area(on a different mobile number of course). If you don't travel much, and are satisfied with Metro service, then this is a very economical and viable solution. As long as you can get an Alltel tech that knows what they're doing...