Why are you so focused on Motorolas?
Because it's documented that some of them work, and the serial interface is accessible through a connector that doesn't have to be bought in 500-piece lots from a single source in Japan (Yes, as a matter of fact, I am still bitter about Sharp screwing Zaurus early adopters by using a connector that only medium-to-large businesses could get during its first year on the market >:().
If you know of a phone (especially one in current production) that has a documented serial interface through a connector that doesn't cost more than the (carrier subsidized) price of the phone, please do suggest it.