I've used a p900 with the little adaptor block on the bottom of it feeding into my autocom.
Works fine, phone in pocket, in goretex bag. Probably work just as well in a tankbag.
Record voice tags for your common callers and it'll announce them as it rings.
Voice dialling is not much cop on the 900 when stationary, and hopeless above 40. You need to say a magic word to wake the phone up, then the voice tag. That coupled with the autocom muting is a bad combination.
I was surprised to find it called out to my parents while riding through Sutton one day, after shouting something universally rude at a car. So be careful if you have tourettes.