The Sena SMH10, this thread, and the customer support at SENA are all awsome. I have had my Sena unit for over a year now. I have an iPhone and a Zumo 550. I never could get it to work correctly with all devices synced so I went back and got info from here and the manual. The problem was I could hear my music and use the phone but not the Zumo. I followed the advise here and in the manual and could get both to work once until I would power off.
Contacted SENA and they have me listening to tunes, talking on the phone, and getting voice prompts from the Zumo. Had to clear all devices from both the Sena and the zumo and iphone. Did a factory reset. Did a firmware install. Followed the syncing instructions from the customer service (which was different from the manual) and success!!!