I'm not really sure what to make of this, it's as though Microsoft plans to not only provide you with a powerful, simplistic handset, but to throw in some Nintendo Wii Remote-type accessories as well if this patent is anything to go by. Should this indeed turn out to be the case, that all future Windows Phone handsets will have a slide-out accessory expansion slot, then it could open up a whole new realm of opportunity.
From the trusty external keyboard that aids typing to a battery extension to a game pad that gives the user an edge in gaming, I'm sure Microsoft has bags of imagination (as anyone would) surrounding this idea. As for me I'm not one to fuss about moving/interchangeable parts as I'm fully aware that hardware wears out. It's one of the reasons why I adore my Samsung Omnia7 - it's just a block with no moving parts (sliding keyboard etc.).
"A mobile communication device comprises a first device with a first display and multiple second devices. The second devices are releasably attachable to the first device and are interchangeable with each other. The mobile device can operate as a mobile cell phone with one or more second devices operable as a mobile phone hand set. The second devices can comprise one or more game controllers, batteries, physical keyboards and/or mobile phone handsets with a display. In a detached configuration, the first device is separated from the second devices and can wirelessly communicate with one or more of the detached second devices. In a three device configuration, the first device can send commands, control signals or content to one or more external devices in addition to the second devices."
It's interesting to note that the secondary devices (accessories for the smartphones) will be able to work wirelessly without being connected to a handset. Still, I remain skeptical. Let us not forget the integration with Kinect we could be experiencing in the future.