said by en102:There's good with both services...
T-Mobile
1. UMA / WiFi service allows for any WiFi connection - which basically works great for cheap international roaming
AT&T:
1. Should be usable on any GSM/3G (assumption) phone that the carrier will allow to use
2. Not as 'portable', as its using carrier licensed frequencies and not 'open' WiFi.
You are both correct in that they are very similar, and accomplish the same task. You also bring up a good point about (international) roaming via UMA. I think the real distinction is that femtocell service is simply an extension of the existing "cellular" network, whereas UMA is more of a supplementary service for specific handsets. Both are good, and I think that people should choose the solution that works best for them and their situation. 
