Brewnut - Here's the deal...
If you have a Zumo, or anything else plugged into Aux, and you have selected Aux as your audio source, you will hear the audio from your aux device, PLUS be able to use Intercom, PLUS be able to use CB. You WON'T be able to hear any other audio option while Aux is selected (e.g. AM, FM, CD, WB, XM), which you would expect. You wouldn't, for example, be able to hear AM while FM is selected. Same idea. If you are following me so far, this should tell you that while in Aux mode, you will be able to hear all options available to you on the Zumo, including turn-by-turn, MP3, and XM. If you do not have Aux selected, because you are listening to a CD, you WILL NOT hear the Zumo's turn-by-turn or any of the other Zumo options. You can, however, keep an eye on the map and the written directions, but you won't be able to hear them. All of the audio options on all of the sources can be heard on the speakers or in the headset.
Here's where it gets murky.
You can pair a bluetooth phone to the Zumo, you can take in incoming call or make an outgoing call, but you will only be able to hear it with the above setup. The party on the other end of your call WILL NOT hear you. The wired microphone is connected to the HD Audio system for use with Intercom and CB, but it DOES NOT connect in any way with the Zumo in order to make phone calls. Just doesn't! That doesn't mean that it can't be done - just means that you have to do more work & spend more money. Here are your options:
1. Find an HD Bluetooth module. Expensive, no longer made, but I'm sure that it works great. Ebay will probably be the only place to find it.
2. Buy a bluetooth headset that pairs to the Zumo. You will then hear your turn-by-turn, and be able to make and receive calls using the headset microphone. Downsides: Zumo does not support stereo bluetooth, so you will have to buy a stereo bluetooth dongle, insert in Audio Out on the Zumo, and pair the headset to it for your music stuff in stereo. Another downside is that you won't be able to hear any of the HD audio options in the headset - only the Zumo stuff.
3. This is the best option. Configure as originally discussed, and buy an after market device that routes the wired microphone to your Zumo when you want to make a phone call. I believe that J&M makes something that will do this, but it costs over $300. One of our members, Jim Bissonette makes one for less than $100. Works great for me. Read through this entire thread, as this topic is discussed in depth - by Jim himself and others.
Let me know if this confused you more.
Ed