Apple iPhone – Internet and MMS (iOS 6 or later)

Go to “Settings”, tap on WiFi and temporarily turn it OFF
Back in “Settings”, scroll down to “Messages” and tap to open it. Make sure MMS is OFF
Go back to “Settings”, tap on “General” and then “Cellular”. Make sure “Enable 3G” is OFF & “Data Roaming” is ON.
Scroll down & tap on “Cellular Data Network”
Under “Cellular Data Network” put in the following:
Cellular Data APN: simple
MMS APN: simple
MMSC: http://smpl.mms.msg.eng.t-mobile.com/mms/wapenc
MMS Proxy: 216.155.165.50:8080
MMS Max Message Size: 1048576
MMS UA Prof URL: http://www.apple.com/mms/uaprof.rdf
Leave all other fields blank
Click on the Home button to go back to the main phone screen
Go back to “Settings” one more time, scroll down and tap on “Messages” and turn it ON
Press the Home button and you’re set to send & receive MMS on SIMPLE Mobile!
Once you have set it up and tested to see it works, you can re-enable WiFi, turn off Data Roaming and turn on 3G (or leave it off if you’re not in a 3G area for AT&T devices on our network).