APN: phone
Username:
Password:
LTE Setup (Optional):

APN: (Leave Blank)
Username: (Leave Blank)
Password: (Leave Blank)

in MMS section:

APN: phone
Username:
Password:
MMSC: http://mmsc.mobile.att.net/
MMS Proxy: proxy.mobile.att.net
MMS Max Message Size: 1048576
MMS UA Prof URL: http://www.apple.com/mms/uaprof.rdf

or there any updated or alternative at&t apn settings for iphone?