I've been through untold iterations of trying to get my Garmin 2820 with bluetooth to work with the Voice II and my bluetooth phone. I spent a lot of time talking with Garmin support. There was one solution that sort of worked. You will find on this forum, topics related to an obsolete/discontinued Motorola product known as the HF-820. I used that for a while but it still was not optimal. So I went in a different direction.
You may want to consider a slightly different direction also. If not, that's okay. Consider this food for thought.
I do not try to interface my Garmin GPS anymore with my phone. The Garmin GPS interfaces with the Voice II just fine (route directions and XM stereo) so that's that.
I interface my bluetooth cell phone to the Voice II through a bluetooth adapter. This one
. The Starcom BTM-01 pairs to your cell phone via bluetooth and connects to the Voice II Phone input via a cable that I ran from underneath my seat (where the adapter is connected to a switched power source) up into the oddiments tray. The cable from the BTM-01 is sized at 3.5mm (stereo). You need to reduce that down to a 2.5mm stereo male plug to connect to the 2.5mm Voice II cellphone jack. The adapter is readily available at Radio Shack.
Other points to consider if you use this method. Your phone needs an auto answer function to answer calls (my Nokia did). Otherwise you have to be able touch a button on the phone or something. To make calls, I had the few numbers I needed on speed dial.
I will face new challenges this year since I got an iphone which I don't think has auto answer, plus the touch screen interface will be a challenge because of the gloves that I wear. Oh well, that give me something to think about while riding.
Attached is a picture of my oddiments box and where I put the the 3.5 to 2.5 plug adapter.
Also, I use the BMW headsets with Voice II. I think they are the same as the J&M Elite series. Both need to use the high end lower cord (Z series? ... I forget). I only mention this because I think somebody mentioned mic volume on telephone call issues. Just something to think about.