The monthly fee is on top of the phone's price — $499 for a model with 4 gigabytes of storage and $599 for one with 8 gigabytes. The phone is slated to go on sale at 6 p.m. local time Friday at Apple and AT&T stores as well as Apple's Web site.

Apple claims the iPhone — which combines the functions of a cell phone, iPod media player and Web-surfing device — will be easier to use than other smart phones because of its unique touch-screen display and intuitive software that allows for easy access to voice mail messages, the Internet, and video and music libraries. AT&T is the gadget's exclusive carrier.

The $59.99 monthly plan includes 450 minutes of voice time; a $79.99 plan includes 900 minutes; and a $99.99 plan includes 1,350 minutes. All three offer 200 text messages, unlimited data services, minutes that roll over month-to-month and mobile-to-mobile calls. There also is a $36 activation fee.

Customers will be able to activate their wireless service from home through Apple's iTunes software, the companies said.

Skeptics question whether even the most innovative product can live up to the iPhone's lofty expectations. Scrutiny of the product is so great that any small disappointment could send Apple's stock plunging, analysts say.

Apple shares dropped $2.72, or 2.2 percent, to $119.62, in afternoon trading. Shares of AT&T gained 63 cents, or 1.6 percent, to $39.71.

Andy Hargreaves, a Pacific Crest Securities analyst, said Apple shareholders have run the stock up in anticipation of the iPhone's release, and they don't feel it will go much higher after the product is available, he said.