I'm using my N810 with on AT&T with a Samsung Eternity so I'm not sure if the settings will be the same. I'll post mine just in case it may help.

In the N810..

Connection type:GPRS
Access Point name: wap.cingular
Dialup number: *99**1*1#
User Name: WAP@CINGULARGPRS.COM
Password:cingular1

Under Advanced/Other.
Allow plain text login: is checked
Use PPP compression and Supplementary AT commands are not checked off.