I didn't see that it required AT&T, just saw GSM, so in theory you could go with Either T-Mobile or AT&T no?
From a different link for the same product: "GTU 10’s tracking capabilities are a result of combining high-sensitivity GPS with a connection to AT&T’s nationwide wireless network"
Link:
http://garmin.blogs.com/pr/2011/01/garmin-gtu-10-new-gps-locator-helps-you-track-whats-important.htmlGo to the first line in tracking options....not that it really matters what cellular network it uses. My point was that it does use a cellular network.