Cingular does this two different ways....
They have the Bytemobile optimization client - which fortunately can be uninstalled from Cingular Connection Manager (it also causes other problems). Additionally one has the option with each of the PC cards that Cingular offers to use the manufacturer's wireless manager instead of Cingular Connection Manager.
They also have two different logins. Depending upon which one you use, you get normal images or degraded images (for faster web browsing).
Personally I hate degraded images, so I'll take the slower connection over fuzzy images.
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No acceleration (qualilty images)
User name --
ISP@CINGULARGPRS.COM
Pass word -- CINGULAR1
With acceleration (fuzzy images)
User name --
ISPDA@CINGULARGPRS.COM
Pass word -- CINGULAR1
Access point or APN is "isp.cingular"