Here is the constellation of components that I have tried to combine without much success.
Garmin Zumo 550
Motorola Razor w/ Bluetooth
I used to use (and will probably revert back to) the original Interphone. It allowed me to communicate with my riding buddy, and with some contortions that I got used to, to toggle to make and receive cell calls.
I wanted to upgrade because I purchased the Zumo 550 which would allow me to play MP3s.
It doesn't work, at least not for me. I cannot make phone calls through my Zumo via the F4. And when I configure the set up to make calls independent from the Zumo, my connection to the Zumo via the F4 gets lost.
My phone conversation with BlueAnt, the makers of the Interphone was unsatisfactory, to say the least. RevZilla, the distributor for the Interphone understands the problem and has agreed to take back the F4 Interphone.
Maybe someone has had better experience with this device than I or, even better, has a better solution.