The bluetooth phone mic has to go somewhere. After a little bit of thought I decided to mount it to the top of the center gauge cluster on the top of the dash. When you take it off there's a big hole that's easy to feed the mic wire through, but then, to avoid having to cut a big, ugly hole in the top of the gauge cluster (the mic on one end, and the 3.5mm plug on the other end, they're pretty big, so would need at least a 3/8 x 3/8" hole to pass through).
So, I notched the front edge of the gauge cluster lid, and opened up the circuit board assembly inside and notched the front of it too, so I could easily feed the wire through all of that, up through the center, and down to the radio. I worried that the exposed wire would look bad, but it seems to be OK.
Oh, crud, some of the photos got rotated sideways and upside down when uploaded here. You can turn your screen over to view them, I guess.
1st photo is the big hole in the dash, under the gauge cluster.
2nd photo is the notch in the circuit board assembly, inside of the gauge cluster (the hole in the center of that which I fed through from underneath is not shown, but it is open to the bottom and easy to feed the wire through).
3rd photo is the notch in the gauge cluster lid, during the test fitting.
4th and 5th photos are the "I hope this will look alright" check during assembly.
6th photo is how it looks to the world. Once the wire relaxed a little it straightened out and was not so wrinkly.
The wire is really, really long (so it could be run up the A-pillar and over the windshield header, if wanted). That location would be more invisible, but looked like a lot of work so I chose this way instead. After wrapping up the coiled up excess, it tucked nicely in behind the head unit.
Dang, there's TONS of spare room in the instrument panel. I am used to working in small cars where fitting accessories is a major chore. You could throw a cat in some of the vacant spaces in there, very nice!