Cingular has a weird structure of their unlimited data plans.

If you have a device that qualifies as a PDA to Cingular, to get unlimited data is $44.99 a month for the "Data Connect Unlimited" plan. This plan is in addition to your voice plan. Any device with a QWERTY keyboard, touch screen, or both, the only way you can get unlimited internet is the Data Connect Unlimited.

They have another plan called "Smartphone Connect Unlimited" which is for a grand total of two Cingular-branded phones made by HTC, the 2125 and 3125. They have Windows Mobile but the only input method is the standard cell phone numeric keypad so Cingular has cheaper data plans for them. The 2125 is a rather chunky bar style phone, the 3125 is a flip. I have the 3125, and I got it specifically because of the cheaper data plan.

Both the Data Connect and the Smartphone Connect do not include text messages, so I tacked on an additional $4.99 a month for 200 text messages.

For "regular" phones you can get various Media Max Bundles that include unlimited internet (but only the basic WAP kind that you get on non-smartphones) and varying numbers of text messages. The cheapest one with 200 texts is $19.99.

So to recap,

PDA = voice plan + Data Connect Unlimited (44.99) + text plan
Smartphone = voice plan + Smartphone Connect Unlimited (19.99) + text plan
phone = voice plan + Media Max Bundle of whatever text message quantity you want (start at 19.99 including 200 texts)