Straight from my AT&T M8. Hope this helps:
Name: ATT Phone
APN: phone
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC:
http://mmsc.mobile.att.net
MMS proxy: proxy.mobile.att.net
MMS port: 80
MMS protocol: WAP 2.0
MCC: 310
MNC: 410
Authentication type: Not set
APN type: default,admin,fota,mms,supl,hipri,dun,att
APN enable/disable: Enabled
Bearer: Unspecified