If you’re curious, and haven’t seen them yet, Apple has posted the AT&T costs and features for the iPhone rate plans. I do not know a lot about cell phone rate plans, but they seem reasonable (or at least on par with the standard rates). For example, the family plan is comparable to what we pay now.

There are more options and plans listed on the Apple site, but here is the basic matrix to get a feel for the plans (taken from the price listing page):

Monthly Price Minutes Unlimited Data (Email/Web) Visual Voicemail SMS Text Messages* Nights & Weekends Rollover® Minutes Unlimited Mobile to Mobile
$59.99 450 Check Check 200 5000 Check Check
$79.99 900 Check Check 200 Unlimited Check Check
$99.99 1350 Check Check 200 Unlimited Check Check

It also seems that you activate and sign up for the plans in iTunes so you theoretically don’t have to go into the store to get one. There is an activation demo video on the site as well.