Look at the top of this Discussion area and see the propaganda posted by Jason L on April 30th:
http://www.att.com/Common/aboutus/files/pdf/emerging_devices/iPad_factsheet.pdf
In particular:
Domestic Data Plans for iPad
Recurring monthly charge with no long term contract
• $14.99 per month for 250 MB • $29.99 per month for unlimited data • Unlimited access – no added cost – to AT&T’s 20,000+ Wi-Fi Hot Spots
How do I manage my 3G plan for iPad?
Can I turn service off or change my plan?
Once you sign up for iPad 3G data service, you can add to or cancel your domestic plan at any time – no penalty. For domestic plans, if you do not cancel, your service will automatically renew every 30 days to provide a more seamless data experience on an ongoing basis. For example, if you activate service on May 9, your service will automatically renew 30 days later with the same plan. If you do make a change, a new 30-day window begins.
What happens if I exceed the amount of data in my selected plan before the end of one month?
With the on-device management system, you can check your data usage in Settings>Cellular Data on your iPad at anytime. Also, for the $14.99 plan, iPad will even let you know when you’re about to reach your 250 MB data limit. You’ll get three alerts — at 20 percent, 10 percent, and zero. With each alert, you can choose to add more data or wait and do it later.
If you do exceed the amount of data in your plan, your plan will expire, but it’s easy to add another one. Also, with domestic plans, you can wait until the 30th day from your purchase when your plan will automatically renew going forward.