Following up on our extensive reporting on a Verizon iPhone expected tomorrow at a press conference in New York, people in the know peer into their crystal ball to estimate the product’s market potency and the impact it’ll have on Apple’s business. For starters, last weekend Reuters reported that Verizon plans on luring the iPhone nation with unlimited data plans, in contrast to AT&T which last year gave up on an all-you-can-eat offering, favoring 200MB and 2GB capped options. Unlike with AT&T, Verizon’s network doesn’support simultaneous voice and data traffic at this time.

AT&T is already making a point out of this as their public relations chief Larry Solomon told Silicon Alley Insider that a CDMA phone isn’t built for speed, warning would-be Verizon defectors to get ready for "life in the slow lane." Apple Insider dissected Verizon’s and AT&T’s service plan offerings and prices, distilled in the below chart.

Meanwhile, The Wall Street Journal chimed in saying the Verizon network is ready for data-hungry iPhone users who strained AT&T’s network in New York and San Francisco, causing a major PR nightmare for the carrier. The paper corroborated the unlimited plan claims:

It wasn’t clear how long Verizon would offer unlimited-data plans. Its executives have said repeatedly that the industry needs to move to some form of tiered pricing – charging different prices for different amounts of data use – as mobile Internet service use rises, but for the moment the carrier is sticking to its existing plans.

Verizon Wireless will host a presser tomorrow in New York to allegedly greet the long-awaited arrival of a modified iPhone 4 version to its network. CDMA wireless components needed to support Verizon’s network cost more than their GSM counterparts so Verizon could end up asking up to $30 more for a subsidized CDMA iPhone than AT&T, warns analyst Mark Moskowitz with J.P. Morgan.

Big media sees Steve Jobs sharing the stage with Verizon’s president Lowell McAdam tomorrow, but the actual device may not find its way to Verizon Wireless stores before end of the month. It remains to be seen whether new Verizon subscribers will help Apple fend off Android which has captured the #2 spot of US subscriber market share, according to comScore’s November 2010 analysis.

Analysts polled by The Wall Street Journal estimate that Apple "will likely sell 9 to 12 million iPhones on Verizon’s network this year," or nearly as many subscribers as AT&T attracted in the 2010 calendar year. Piper Jaffray analyst Gene Munster estimated AT&T’s 2011 iPhone sales in a Monday note to clients at eleven million units versus nine million from Verizon.

These estimates, if true, don’t bode well for AT&T since they could be read as a whooping 6.5 million cannibalization for AT&T which could sell about 17.5 million iPhones in calendar year 2011 if the iPhone didn’t debut on Verizon. The nine million iPhones on the Verizon network in 2011 would represent 36 percent of an estimated 25 million smartphones for the carrier in calendar year 2011.

Watchers say AT&T is ready for the loss of exclusivity and is bracing for impact. The carrier has been prepping for this for a long time, pundits argue, as it’s been gradually turning the spotlight away from the iPhone and promoting a wide variety of devices from other vendors, including flagship Android phones.

Defecting to Verizon won’t be easy for the existing AT&T customers locked into long-term plans, especially folks on family plans. Be that as it may, the iPhone’s arrival to the nation’s #1 wireless network might slow down Android’s growth, but Apple may not enjoy substantial benefits until after two years, when everyone’s out of their AT&T contracts.