I got MMS working on T-Mo network. I take no credit for this, I got the settings from punkrocknerd.com
Setting up the handset:
On the handset, press Start.
Scroll to Settings and press the Joystick.
Scroll to Connections and press the Joystick.
Scroll to GPRS and press the Joystick.
Press Menu.
Scroll to Add and press the Joystick.
Scroll to Description and enter T-Mo MMS.
Scroll to Connects to and scroll horizontally to WAP Network.
Scroll to Access point and enter wap.voicestream.com.
Scroll to User name and enter . Otherwise leave this field blank.
Scroll to Password and enter . Otherwise leave this field blank.
Press Done twice.
Press Menu.
Scroll to Advanced and press the Joystick.
Scroll to WAP connection and scroll horizontally to T-Mo MMS.
Press Done.
Press the red End Call button.
Setting up the MMS profile:
On the handset, press Start.
Scroll to Messaging and press the Joystick.
Scroll to Multimedia Messages and press the Joystick.
Press Menu.
Scroll to Options and press the Joystick.
Scroll to Account Settings and press the Joystick.
Press Menu.
Scroll to MMSC Settings and press the Joystick.
Press Menu.
Scroll to New and press the Joystick.
Scroll to Name and enter T-Mo MMS.
Scroll to MMSC URL and enter
http://216.155.174.84/servlets/mms.
Scroll to WAP gateway and enter 216.155.165.050.
Scroll to Port and enter 8080.
Scroll to Connect via and scroll horizontally to WAP Network.
Press Done.
Scroll to T-Mo MMS and press Menu.
Scroll to Set as Default and press the Joystick.
Press the red End Call button to return to the main screen.
The handset is now configured for Multimedia Messages.