just completed an early version of MicroBridge [url]http://romfont.com/2011/05/15/microbridge-adb-support-for-arduino/[/url] for .NETMF devices, called FezBridge. Android Debug Mode is available on almost every Android phone and has the same functionality as Android Open Acessory.
Video can be found here:
I second the awesomeness. When Google announced ADK, I got quite excited, but that quicky turned to frustration after learning it only works on a very few hardware/OS combinations currently in use.
Yes ADB is the alternative method for accessing external hardware from Android with USB. It should be possible to combine both drivers ADK and ADB into one. First try to get a connection with ADK then fallback to ADB.
@ Robert (Foekie) . Yes robotics with an Android phone is on my todo list. You get WLAN, Bluetooth, GPS, compass, Onboard Video, Touch graphics TFT and a lot of computing power