RichG--I don't know specifically how AT&T has programmed their equipment. (Each carrier using tri-mode equipment can have its' equipment programmed to do a lot of different things, so you can't generalize any more---gone are the days of just A/B roaming)!

Boomer, several other companies have one-rate programs (BellSouth, GTE, Bell Atlantic). All require you to live in a service area of theirs to provide the service. Check for home service quality b/c it is the single place you'll spend the most time.