All iPhone service plans include Visual Voicemail and unlimited data — Internet and email — so you only have to decide how many minutes and SMS text messages you need. You’ll select your plan when you activate your iPhone using iTunes on your computer.
Existing AT&T Customers
If you’re an existing AT&T (formerly Cingular) wireless customer and you want to keep your current voice plan, you just need to add an iPhone Data Plan. (This may replace your current data plan.) The iPhone Data Plan gives you Visual Voicemail, as well as Unlimited Data—includes both email and texting, all for as little as $20.
Check AT&T coverage in your area.
AT&T is the exclusive carrier for iPhone in the United States — which means you’ll gain access to the country’s largest digital voice and data network.
FROM: http://www.apple.com/iphone/easysetup/rateplans.html
