Most people are pretty defensive about their smartphone choices, with heavy texters defending the BlackBerry's physical keyboard, while others want something with a bigger screen for multimedia. Microsoft however, sees a future where one phone can be all things to all people, by simply swapping out a module to match the occasion.
Their concept is a slider phone, where the lower half is a tray that can hold any one of a number of different modules. Let's say you're going to be on a long plane trip and want to answer a bunch of email messages, then slip in the QWERTY keyboard and start typing. Going camping for the weekend far from the nearest power outlet? Then slide in the extra battery pack. Other possible modules include a gaming controller, and a second display panel to make it into a dual screen phone.
This sounds like a great idea if they can make it work. It does seem like it would be tough to make something like this robust enough to withstand the wear of daily use with all of the required contacts and sliding parts, but those issues can probably be solved. Losing the spare modules is another issue, but I'm sure they would be happy to sell replacements for a price. I can even see a market for specialty aftermarket modules, such as interfaces for specific models of car.
This isn't the first concept like this we've seen, but with Microsoft's muscle behind it, it might actually stand a chance of turning into a real product.