If it's a hit, then it will show that the iPhone — which did so much to define and popularize the smartphone three years ago — can evolve in ways that continue to fascinate consumers. But if sales aren't spectacular, then it would suggest that the iPhone has become just another device in a field that now includes scores of innovative rivals,including many powered by Google's Android operating system.

Verizon and Apple declined to comment for this story.

Some 61.5 million people in the U.S. own smartphones. And in that crowd, the iPhone is "still the iconic device; it's the device to beat," says Roger Entner, founder of Recon Analytics.

U.S. consumers have bought a total of 89 million iPhones vs. 47 million Android phones, a tally that includes devices from different manufacturers and wireless providers, according to financial services firm Piper Jaffray.

But the iPhone is no longer the hottest seller: Some 33 million phones sold in the second half of 2010 were powered by Android, beating iPhone's sales of 29 million, Piper Jaffrey says.

Will Verizon make the iPhone No. 1 again? The devil, of course, is in the details — many of which likely will be made public at Verizon's press conference at New York's Lincoln Center.

For example:

•How much will Verizon's iPhone cost? Wireless providers typically subsidize the prices to entice consumers to commit to multiple-year service plans.

AT&T covers about $400 of the cost of an iPhone when people also sign up for two years of service, Citadel Securities analyst Shin Ying estimates. Consumers end up paying $150 for an iPhone 4 — the latest model—with 16 MB of memory. (AT&T dropped the price to $100 for Black Friday, the big holiday sales event that takes place the day after Thanksgiving.)

•Will Verizon charge a single price for unlimited Internet usage, or make heavy users pay more?

This could be a big differentiator. In June AT&T stopped offering all-you-can-eat pricing to new customers. Under the new system, the company said, most users would pay less while people who frequently use their phones to watch Internet videos and download files would pay more. But that move has been unpopular.

"After years of being conditioned to expect unlimited data, customers simply don't like usage caps, even when they might save money," says Bernstein Research analyst Craig Moffett.

•What features will Verizon's iPhone have, or lack, in comparison to AT&T's?

Verizon's model may not work overseas. The company uses a transmission technology, called CDMA, that isn't found in most other countries, which use GSM technology. To operate abroad, then, Verizon's iPhone would need a different transmission technology, which likely would drive up the cost.

Verizon's technology also makes it hard to let users simultaneously access certain data applications, including GPS directions, while talking on the phone.

AT&T believes that consumers will end up preferring its technology. It's typically faster than Verizon's, even though AT&T has been plagued by reports of dropped calls and uneven coverage in cities including New York and San Francisco. "The iPhone is built for speed, but that's not what you get with a CDMA phone," says AT&T spokesman Mark Siegel. "I'm not sure iPhone users are ready for life in the slow lane."

•Speaking of speed: will the iPhone work on Verizon's speedy new 4G network —or the somewhat slower 3G one?

Going with 4G "would be a significant leap of faith on Apple's part," says Dan Hays, a partner at global telecom management consulting firm PRTM. The faster system still doesn't reach all of Verizon's markets. In the complicated process of juggling transmissions between the new and old systems, "you could wind up with slower than anticipated connections, dropped calls, and spotty coverage," Hays says.

Apple watchers say that the company likely will play things safe.

"The fact that (the introduction) is not in Cupertino (where Apple is based) says an awful lot about what this product will be," says Michael Gartenberg, an analyst with Gartner, a technology research and consulting firm. "If it were anything revolutionary in terms of the iPhone or the iPhone ecosystem, this would have Apple's hand all over it."

'Pent-up demand'

Still, many people are excited by the prospect of using the most popular smartphone on the most popular wireless network.

"There is so much pent-up demand for the iPhone on Verizon, the market share advantage goes to Apple for the next six months," says analyst Gene Munster of financial services firm Piper Jaffrey.

He forecasts that Verizon will sell about 9 million iPhones in 2011, accounting for about 36% of all the wireless company's smartphone sales.

Verizon customer Rachel Sprung says that she's "jumping at the chance" to snag an iPhone. "This is like a holiday and birthday for me," says the 21-year-old Boston University student, who switched to an Android phone last week after using a BlackBerry for several months.

"Everything that goes with an Apple product — interface, sleek design and a Verizon network — is so appealing to me."

Some analysts say that there are a lot of people like Sprung. As a result, "Apple will be the big winner and take Verizon along for the ride," Entner predicts. "AT&T will be struggling. No doubt about it."

If that's right, then it could hit Google and Research In Motion's BlackBerry hard. Android devices and the BlackBerry Storm phone have sold well because they were the best alternatives to the iPhone, says Gartner analyst Ken Dulaney.

He now expects to see "a wave" of AT&T customers who will buy their way out of iPhone contracts and switch to Verizon. "They've waited two years for this, and are willing to spend extra to make the move," Dulaney says

Others aren't so sure.

For example, Danny Chung, 23, a social-media associate in the New York fashion industry and erstwhile BlackBerry user, says he plans to wait to "see how Verizon's network performs with so many people joining because of iPhone."

Several analysts also say that the soaring adoption of Android phones shows that consumers haven't just waited for Verizon and Apple to team up.

"Android has largely caught up to the capabilities of the iPhone and has a wider variety of designs and manufacturers," Hays says. Indeed, he adds, Verizon may discover that lots of consumers will come to its stores to examine the iPhone but walk out with a different model, especially if the Apple device won't handle 4G. "There could be a substantial halo effect for Verizon's other devices."

What's more, consumers who are tied to a two-year contract can't easily switch carriers. Munster says that some 80% of AT&T customers are on a family or corporate plan, which also make it hard to jump.

"If you just bought an iPhone 4 and are in a two-year contract, unless you're very frustrated, you're unlikely to remotely consider leaving to get to Verizon," Gartenberg says.

And AT&T has been preparing for the end of its exclusive deal: When the iPhone 4 was introduced last year, the wireless company made it easy for customers to upgrade their phones. It also has bulked up on rival models that use Android, Windows Mobile 7, and BlackBerry operating systems and steeply discounted many models during the holidays.

If the Verizon iPhone proves to be a dud, then a lot of people will second-guess Apple CEO Steve Jobs' decision to introduce the iPhone exclusively on AT&T.

That deal seemed to make sense for Apple: AT&T was so eager to offer the iPhone exclusively that it agreed to sweet revenue-sharing terms with Jobs' company.

But other providers including Verizon, Sprint Nextel, and T-Mobile also wanted in to the smartphone market. And Google, for one, was happy to fill that vacuum. "Apple made the mistake of letting the genie out of the bottle by letting Android happen," Munster says. "It will be interesting to see if you can put the genie back in the bottle."