One of the most striking trends in smartphone designs is the push towards ever-larger screen sizes. Not only has average screen size increased steadily since 2008, the so-called "phablet" market is poised to explode. Nearly 26 million crossover devices shipped in 2012, with an estimated 60 million shipping in 2013 and 146 million by the end of next year. That's a huge growth rate for a market at a time when both tablet and smartphones are growing more slowly than in past quarters. But what's really surprising about phablets is that manufacturers continue pouring money into the category even as the devices grow increasingly unwieldy for many of the basic functions of a smartphone. We've dug into the trends behind this push