I have Zumo 550. It syncs with the Sena SMH10 as a "selective phone pairing" (i.e. using the HFP protocol).
I also pair the Zumo with my phone, also using the HFP. Then I pair the Sena with the phone using the "selective phone pairing" i.e. AD2P so I can listen to music in stereo (the Zumo 550 does not have stereo BT / AD2P).
This works very well. All phone interactions are with the glove-friendly Zumo. Pausing, resuming, FF and RW over AVRCP works correctly from the Zumo to the phone. When the GPS has to give directions or do phone stuff, the Sena will pause the media device (i.e. phone's mp3-player). I can use the Zumo's MP3 player as well, but it is in mono. Good for books on tape. Or, I can hardware it ... and get stereo. But that's a wire ... which I avoid ;-)
It's a great solution - the best I've seen yet. Many here swear by the Autocomm, and it has its strengths, but the high cost and extensive installation process (compared the Sena) makes the Sena a no-brainer.