I Recently was playing with my Android.
After installing a new ROM I noticed my data network was not working.
After some searching around I found the following:
Basic Settings
AT&T
APN: wap.cingular
Username: WAP@CINGULARGPRS.COM
Password: CINGULAR1 (must be in CAPS)
Expanded Settings
Name: AT&T
APN: wap.cingular
Proxy: leave blank
Port: leave blank
Username:WAP@CINGULARGPRS.COM
Password:CINGULAR1 (yes this is in CAPS)
Server: leave blank
MMSC: http://mmsc.cingular.com
MMS Proxy: wireless.cingular.com
MMS Port: 80
MCC:310
MNC:410
APN Type: leave blank