There have been rumors speculating T-Mobile's implementation of a 3G at least since they made the announcement two years ago. But they have time to catch up because AT&T's 3G network is still premature and is expanding. Last time I tried it, it didn't feel that much faster than EDGE (even though it was).
Plus, there are several issues with phone companies that include 3G in their devices at the moment, one of the biggest ones being battery life. When I used the Treo 750 on AT&T's network (a somewhat expensive two weeks), battery life with HSDPA ON would pitfall to less than half a day or so (14 or 15 hours, but this was with Direct Push on). Furthermore, it was still subjected to high latency, making web browsing on my computer (through tethered connection) just as slow as EDGE, which has lower latency (or did I mix this up?).
If T-Mobile rolls out 3G service, hopefully they do it like UMA and do it right instead of doing it fast.