Often when we say hack it is rather meaningless, but in the case of WPbots.com they deserve all the respect they can get.
The folks over there have figured out how to turn the audio jack into a USB interface for Windows Phone 7 allowing all kinds of peripherals, including a robot they are working on, to be controlled directly from their Windows Phone.
Use the audio jack of the smartphone to convert it into a bidirectional RS232 port. The Windows phone jack has 1 microphone input and 2 audio outputs (stereo Left + Right), so, there is everything we need.
The solution is similar to the Square credit card reader on the iPhone and iPad, meaning Windows Phones have at least one universal interface available on all handsets.
Read more about their plans for Windows Phone robot domination at WPbots.com here.