My uma sucks... and is good also
Love it because my family went from using about 2000 minutes a month to about 200 so it more than make"s up for the cost because I could drastically lower my minute plan.
On the other hand i drop my calls every freaking time I'm on the phone and leave the house. None of our phones hand off the signal well and we all have blackberries.
I also don't think the intenet browsing is any faster at all while i'm on UMA. maybe it's just my area because I hear people all the time on here saying they browse faster and they have a better signal strength using UMA.... but i find it no different at all.
i think it all depends where you live. It's an ADD ON FEATURE so you can alays just try it out and then cancel if you don't like it. downside is if you buy a specific Wifi phone then it still works with regular service but maybe you passed on another phone with you might have liked better had you known you weren't going to use the wifi.