Do you have an ATT SIM ? If so, here is what works for me, granted my S3 is an unlocked i747.
APN -wap.tracfone
Port - 80
MMSC- https://mmsc.cingular.com
MMS Proxy 66.209.11.32
MMS Port 80
MCC 310
MNC 410
That's it, and it has worked since Dec. However, lately I have been experiencing ye old...