I had a Lumia 710 with "4G" but have upgraded to a Lumia 800 (international edition) which only works on T-Mo EDGE (for the moment).
T-Mobile is refarming 1900 to 3G for all cities with LTE. Since I live in San Francisco, I expect we'll be one of the first to have 3G on 1900 MHz later this year.
But even on EDGE, the experience of the 800 is worth it, even compared to the 710 (which simply lacks the great design, crisp screen, and overall hardware experience).
I'm a heavy user, and since most T-Mo people aren't on EDGE anymore, I get the EDGE data stream to myself. I'm averaging about 250 to 300 Kbps, which won't set any new records (but is plenty fast for browsing, streaming YouTube, listening to Spotify/Zune, etc.) And the speeds will get faster, soon.
(For comparison's sake, my "3G" HTC Arrive on Sprint averaged about 130 Kbps on Sprint's overloaded EVDO network, and at a 100% higher cost than T-Mo's $49.99 all-you-can-eat Value plan.)
I've also heard good things about using the Lumia 800 with StraightTalk's "bring your own device" AT&T SIM program, but tales of people losing their numbers and being immediately shut off for passing a secret arbitrary data usage pattern scare me.