To Add or Modify the text messaging (SMS) service center number:
- From the main screen, dial **5005*7672*+12063130004#
- Press Send to set the SMSC.
- Note: To get the plus symbol, press and hold the 0 (zero) key.
- Turn the device off and back on.
To display the SMSC number:
- On the iPhone, dial the following:
- Press the Send key.
- Verify on the display that the SMSC number is programmed correctly on the device.
The above are the correct SMS/MMS/data settings for an unlocked iPhone 4S, but since T-Mobile cannot guarantee this to work on a non-T-Mobile phone, the addition of a trusted third-party MMS application may be needed as well.
I hope this is of some help.
After purchasing my factory unlocked iPhone 4s, I discovered MMS and Facetime did not work. Here is the solution I used to fix MMS, which also corrected the Facetime issue. I followed the instructions from this link http://leimobile.com/tag/ios-5-0-1/ to solve the issue without jailbreaking the phone. It was seamless and worked perfectly. Best of luck!!