AT&T is pushing their 3G data plans for the iPad and iPad 2 with an offer of one month free on their top-level 2GB data plan for the devices. The 2GB plan normally goes for $25 per month and of course there’s no contractual commitment – you can start and stop the plan each month as desired.
According to TUAW, you need to either visit an AT&T store or call 1-888-237-5888 to take up this free month offer. You can’t do it on the iPad itself.
Doing this will sign you up for an auto-renewing plan for 2GB at $25/month. If you want to cancel you’ll need to do so within 30 days of activating the plan. You should be able to do that on the iPad itself or by calling into AT&T.