After six months of hints and hype, Apple Inc.’s iPhone goes on sale tomorrow. It looks like it will become a must-have for millions, and whether it sells as well as expected or not, it marks a revolution into a new form of smart-phone technology.

AT&T and Apple, whose retail stores are the only sales outlets, are looking for a huge success. AT&T has hired 2,000 extra clerks to handle an expected horde of buyers. Apple’s CEO Steve Jobs predicts 10 million users by the end of 2008. (Sorry, but none of the stores are listed in Maine.)

The iPhone, a sleek instrument about the size of a deck of cards, is billed as a super cell phone and a lot more. Mr. Jobs calls it the best iPod ever made, a great cell phone, and “the Internet in your pocket.” The reviews, while generally positive and some even fawning, have liked some features and questioned others.

Apple has been making improvements right up to the sale date – extended battery life and a display screen cover of glass instead of scratchable plastic. Last-minute secrets may be disclosed. A Global Positioning System probably won’t be available at first, but Apple and AT&T are said to be working on it.

The iPhone works with a touch screen, which has been replacing the mouse in restaurants and at checkout counters. A touch of the finger can dial a phone call, take a picture, open a newspaper, open a Web site, get a weather prediction, find a place on a map or satellite view, start music on iTunes, or send an e-mail or text message. A 20-minute video on the Internet will tell you a lot more.

So what’s the downside? The only carrier is AT&T (formerly Cingular), and there are folks who hate that system and would prefer Verizon or something else. Apple may seem unfamiliar to the many who use Microsoft personal computers with the Windows operating system, although Apple’s wildly popular iPod has drawn millions to the Apple brand. It won’t do much for the hard of hearing, and it probably won’t replace the laptop.

A 14-year-old consultant who is a whiz on the computer and a big user of text messaging and iPods says she would like to have an iPhone despite the cost but probably won’t, for fear of becoming obsessed with it. She fears that she will lose contact with friends who get the iPhone because they will have everything they want all in one box and may lose the use of their vocal cords.