While browsing the AT&T website, I stumbled upon three additional iPhone rate plans that weren’t previously announced:

Most people will choose from the first three service plans, but those of you who demand more minutes can upgrade to 2000, 4000 or 6000 minutes for $120, $170 and $220 respectively.
In addition, the AT&T page (click the PLANS tab beneath the iPhone logo) reveals that additional SMS text messages will cost you $10 for 1500 texts or $20 for unlimited.