Sorry, I didn't say this clearly.
Two comments:
... could build a new kernel image, and put whatever I wanted in ...
if it is very useful, it usually gets done within a few months, so don't assume you have to DIY a kernel
(I have a 'theory' about Google doing the complement to advertising, ('opportunitising' ?) where Google detects common needs based on searches, and pushes relevant ideas towards folks who may be able to exploit opportunities, but lets ignore that for now :))
... but it isn't clear that Android phones can support USB host or USB OTG
AFAIK, USB OTG is a different socket, so if the phone doesn't have it, it doesn't matter what the software does
So if Blair C wants to use USB, it may need a USB intermediary to integrate two slaves.
Hence, Bluetooth seems to be a simpler path, even though, IMHO Arduino Bluetooth is over priced (e.g. dealextreme have Bluetooth for $1.98)
GB