Compiled from other posts on this forum (Thanks guys). This worked for me with firmware 2.1 on Tmobile with T-Zones
Previously I had the T-zones hack installed from Cydia. If you have this do the following steps to use the new apn otherwise skip down to step 6.
1. From cydia, remove T-Zones hack, exit Cydia
2. Go to Settings->General->Reset and select Reset Network Settings, this will force a reboot.
3. Go to Settings->General->Network->Cellular Data Network. type the following:
APN: epc.tmobile.com
Username: (leave blank)
Password: (leave blank)
4. Do a full reset of the phone.
5. With WIFI off, Open Safari and verify you have internet working. It takes about 1-3 refreshes to work the first time.
6. From Cydia, install SwirlyMMS (latest version: 1.2.9), requires a reboot.
7. Open swirlymms, click DEMO, then OK to get license, after click DONE, then the RIGHT ARROW to go into the swirlymms program main window.
8. From SwirlyMMS, click on settings on the bottom middle and put in the following information (may be case sensitive)
MMSC: http://216.155.174.84/servlets/mms
Proxy: 216.155.165.50:8080
APN: wap.voicestream.com
Username: (leave blank)
Password: (leave blank)
Image size: High
serAgent: SE_W800i
click save.
9. Click on the Compose icon on the bottom left and type in your cell phone number and send a MMS to yourself to verify both outgoing and incoming messages work.
Good luck,
Swakel