CDMA Two of us traveled from IL to OK and back (1000 me) with three cell phones: AT&T GSM, VZN iPhone, and Sprint CDMA.
Sprint and VZN worked all the way down. iPhone worked all the way down. AT&T in most communities but not in-between. My cousin used my Sprint most of the time and played games on iPhone. It was the same thing returning except when we stopped at Rolla, MO., a small college town. Only AT&T worked.
Sprint and VZN roam on each others CDMA towers - although VZN claims they own the towers. Without roaming enabled Sprint doesn't work well outside of Chicago. in a US Cellular saturated state like IL. T-Mo doesn't work in USCellular either.
iPhone users have the same problem locked or not. The $30 Apple plan is what is unlimited: that's iTunes. Anything T-Mo provides is added cost -- at VZN. I paid $10 bucks for the same free 1000 messages Sprint charged $1. And tech support at Sprint that was 100,000 times, friendlier and more helpful at Sprint. I just dumped VZN. If I ever go back to a contract phone I'll go to Sprint. I would go to T-Mo too except it does not work well in rural America, either.
Mac: No windows, No Gates, Apple inside