It's a foregone conclusion that Apple's (Nasdaq: AAPL) iPhone 5 will be big when it rolls out in a few weeks. FBR Capital Markets analyst Craig Berger turned heads earlier this month by forecasting that Apple may sell as many as 250 million units during the iPhone 5's lifetime.

Okay, but how big will it really be?

Screen size has become a battleground.

It may not seem that way to iPhone owners. They seem to be perfectly fine with the trendsetting smartphone's 3.5-inch touchscreen. However, given the success of Samsung's 4.8-inch Samsung Galaxy S III -- and yesterday's introduction of the 5.5-inch Galaxy Note II -- it's clear that size does matter.

One of the reasons why Google's (Nasdaq: GOOG) Android has grown so quickly as the mobile operating system of choice -- going from a global market share of 43.4% to 64.1% over the past year -- is that the open-source nature of the platform frees handset manufacturers to perpetually push the envelope. Yes, Samsung's the one that came up short last week in Apple's patent case, but the flow of fresh Android gadgets still provides a sharp contrast to Apple's annual updates.

It's not just Android phones getting bigger, of course.

Samsung also became the first company to officially introduce a phone running Microsoft's (Nasdaq: MSFT) Windows Phone 8 yesterday. Beating Nokia (NYSE: NOK) to the punch by a few days -- though the devices will probably hit the market at the same time -- Samsung Ativ S will come packing a 4.8-inch display.

Some speculate the Apple's iPhone 5 will be bumped up to a 4-inch screen, but that may not be enough. There's a much bigger display size difference than what's suggested by 3.5, 4, and 4.8 inches.

It's understandable if Apple doesn't want to play the "phablet" game; going as big as the stylus-saddled Galaxy Note II would be too big a gamble for Apple. However, we're clearly no longer living in a "one size fits all" world. The speculation that Apple will crank out smaller iPads and larger iPhones won't die until either the company gives the market what it's expecting, or consumers decide that size really doesn't matter.

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Longtime Fool contributor Rick Munarriz calls them as he sees them. He does not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.