It seems Microsoft has patented a phone with a cavity in its slider. In that cavity you can add a swappable accessory such as an additional battery, controller or anything else that fits that form factor I suppose. Besides the obvious of how cumbersome it would be to carry multiple accessories it seems interesting but given their track record with previous phone designs I'm not getting my hopes up.
Here's the link: http://www.engadget.com/2011/09/23/microsoft-patents-modular-windows-phone-with-swappable-batteries/
Here's the link: http://www.engadget.com/2011/09/23/microsoft-patents-modular-windows-phone-with-swappable-batteries/