In case it helps anyone else, I was able to get UMA working on my curve. Thanks for the tips.

My landlord has a Netgear WPN824v2 wireless router with mixed b/g and WPA TKIP on Comcast cable. I live in his basement, where my signal is very weak - my laptop barely works. I installed dd-wrt v24 micro on a Linksys WRT54G v6 in 'repeater' mode ('client bridge', 'repeater bridge' didn't work). Now I can use UMA fine. I am on a sub-lan. Call quality is great. I was very surprised, given my router is a 'neutered' one where only a scaled down dd-wrt works.

This T-Mobile UMA service is really great. Most of my calls at work and at home are through the Wifi.