There are only contract ones out there. Not sure on how 'cell' phones work in the US, but if it is the same as here you will pay per Kb of data transfer onto your monthly statement.
in order to enable the phone you have to have service from at&t and that service includes using the built in web browser so your paying for the contract not th internet per say
As said, if it is anything like here, you have to pay for the WAP as an extra per KB (Unless it has some free internet minutes.) This is not via the 802.11b/g where they can't charge for it.