My experience is similar, but distinct. I have a Zumo 550 and an Autocom. With my prior phones hardwired in, the phones worked perfectly. No one could tell that I was riding unless I informed them. However, I could not use the Zumo's phone book or dial out or even refuse to answer a call.
On my current phone, I can hook it up through BlueTooth, and have the opposite experience. All the Zumo features work, except nobody can hear/understand me. For the most part, I can hear them okay. The phone does work with the engine and bike stopped, however.
Don't know if any of that helps. I've sort of gotten to the point where it's nice not to make or get calls when riding. Sometimes, when traveling with a group, it would be nice to be able to coordinate better w/o stopping, but we manage.