This worked for my at&t S3Name: straight talk
APN: att.mvno
Port: 80
MMSC: http://mmsc.cingular.com
MMS Proxy: mms3.tracfone.com
MMS port: 80
Mcc: 310
MNC: 410
Authentication type: none
APN Type: default,supl,mms
APN protocol: IPv4
Tip: no spaces in "default,supl,mms"
Good luck. Not sure bout...