AT&T only has 4 APN's and none of them let you bypass throttling.
wap.cingular APN Type: <blank>
Phone APN Type: default,supl,agps,fota,dun,
Broadband (for tethering) APN Type: tether, entitle
MMS APN Type: MMS
A lot of people default to wap.cingular since the newer APN's are function specific.
Throttling is based on your SIM card's serial number.
Changing your APN will do nothing.