jbwhip,
I have a v360 and the same t-mobile plan. I just got connected.

1) I ran the 'configerator' at http://tmobileus.wdsglobal.com/phonefirst
2) I deleted my old phone connection from 770/ctrl panel/connections and from 770/ctrl panel/phone.
3) I ran the wizard in 770/ctrl panel/phone
4) I entered the information from the above thread which I copy here from Neil Speer:

Access point name: wap.voicestream.com
Dial-up number: *99#
User name: leave blank
Password: leave blank

Click the [advanced] and check "Use Proxy"
HTTP Proxy: 216.155.165.50
Port: 8080
HTTPS Proxy: 216.155.165.50
Port: 8080

Click [OK] and [Finish]

It worked! I get about 260k/s

Bruce