yes, I have the 6680, and it is a wonderful phone.... works nice on virgin, but no email (comming soon.. ) I might get t-mobile just for the email access...
only thing about 3, it works when it works, and when it doesnt, its a POS....
I dont have 3, but a lot of people got the 6630 on 3, and thought the phone was *totally crap* -- then they switched to T-mobile, switched off 3, and found it a quite nice phone....

moral of the story, it may be a bit more expensive 'sim-free' , but *you* get to choose what works, not your provider....