The original press release at either AT&T or Tmobile's website mentioned a 5 year roaming agreement for Tmobile users. I rarely get to Starbucks and ever more rarely use my phone there, but I am fairly sure you can still use UMA on an 8320 at Starbucks. If you look up the Hotspots on the Tmobile coverage map, you'll see lots of Starbucks locations there.
Here's a Tmobile mention from February 2008: https://www.t-mobile.com/company/Pre...+and+Starbucks
"...Even after the transition, T-Mobile HotSpot and HotSpot@Home customers will continue to experience seamless Wi-Fi access at Starbucks locations for at least the next five years under
a roaming agreement between T-Mobile USA and AT&T. .."