FaceTime on T-Mobile US

I recently moved to San Francisco with my iPhone 4. My iPhone is factory unlocked as it was bought in the UK. I went into the AT&T store and i wasn't a fan of the plan they were outlining for me, so i went across the street to the T-Mobile store.

I got a T-Mobile plan, and they nicely cut the SIM card up for me so that it would fit into the iPhone 4. Once my phone was activated, i managed to get rid of the voicemail notification.

I couldn't get FaceTime to work on T-Mobile.

One night while i was talking to a friend, he told me to try turning FaceTime on again. Previously this had not worked, so i wasn't very hopeful. However, this time it worked. I didn't understand why, but i made and received several calls with FaceTime working perfectly.

Tonight, i popped my old O2 SIM card into my iPhone to check on my messages. After i put my T-Mobile SIM back in my phone the FaceTime buttons were gone.

Here's the list of actions i took, and i now have working FaceTime on my iPhone 4:

1. Turn phone off and on—can't hurt right?
2. Ensure that you have WiFi, and the FaceTime switch is turned off.
3. Go into General, then Network. (My settings are Enable 3G: Off, Cellular Data: On, and Data Roaming: Off)
4. Go into Cellular Data Network.
5. For the Cellular Data APN enter epc.tmobile.com.
6. For the MMS APN enter epc.tmobile.com.
7. For the MMSC enter https://mms.msg.eng.t-mobile.com/mms/wapenc.
8. For the MMS Proxy enter 216.155.165.50:8080.
9. For the MMS Max Message Size enter 1048576.
10. For the MMS UA Prof URL enter http://www.apple.com/mms/usprof.rdf.
11. Go back to the first pane in the Settings application.
12. Restart phone.
13. Go back into the Settings application, go into Phone.
14. Switch the FaceTime switch to On.

After this, it should say "Waiting for activation" below. About thirty seconds to a minute later, mine changed to "Your phone number will be shared with people you call with FaceTime.", which i believe means that it is working. I tested via FaceTime on my Mac, and that was fine.

This seems to have worked for me twice. I can't guarantee it'll work for everybody.

To verify, here is a picture of my Settings application once this has worked: