T-Mo compatible or AT&T???
I'm going to guess you went with the AT&T compatible...
Call up the dialer pad > tap the upper left for the App menu > Preferences and Accounts > scroll down to Manual Settings and turn that ON > tap Edit Network Settings
On the APN tab enter tfdata for APN and leave everything else (user name, password) blank. Tap the Change Settings button.
If you get an error saying the settings are incorrect, tap Set Up Anyway.
On the MMS APN tab enter tfdata for the MMS APN. Leave user name and password blank. For MMSC enter
http://mms-tf.net and for MMS Proxy enter mms3.tracfone.com:80
Since there is no spot for Port you have to use colon ( : ) 80 at the end of the MMS Proxy string.
Max Size, I dunno. Try leaving it at the default of 600.
If you get an error saying the settings are incorrect, tap Set Up Anyway. Test MMS by trying to send/receive a text with a picture attached...
If you have the T-Mo compatible SIM try following that pattern with the T-Mo comp. settings here:
Support | NET10 and use the ones for Smart Phone.