i have a iphone 4s (ios 8.3, now 8.4) and a lumia 822 (recently updated to Win 10).  my win phone is using tfdata, and when apn installed, mms works both ways.  iphone is set to att.mvno and would not send or receive mms, but internet works.

after much reading someone suggested (here: http://apple.co/1LM7pLw) that you could call ST and have them change your carrier from att.mvno to tfdata.  they claimed that was the issue, and many here seem to confirm if you switch to a SIM with tfdata, everything is fine.

i called them and after transferring a few times i got someone who said he would try to have that done, then call me back.  well they called and left a voicemail to see if my issue was solved, but it was not, since they never changed anything.

spent another hour on the phone with someone who wanted to try something that worked for a similar case a few months back.  didn't work, so he said he would change me to tfdata.  after that i could send MMS using the tfdata apn, but i could not receive them.

interestingly when i go to ST website and enter my phone # it tells me i am still to use att.mvno, not sure if that part of the system just hasn't updated yet or what.  previously internet would not work at all using tfdata settings.  now after the change he made i can use internet and send MMS using TFDATA or with NO PROFILE, and oddly if i use att.mvno, i have NO NET, but i CAN SEND MMS.

no matter what i do i still cannot receive MMS.  i just renewed my service, so i'd wait until that ended to try getting a new SIM.  i think it's just a bit more money to get the SIM extra with a month of service anyway.

so my situation seems to be an odd one.  if anyone has any advice, suggestions, or insight into this, please let me know!  thanks!