I have a Garmin 2720, works great, but no bluetooth, I have the mounting system/cradles/connections all set up for my 2720, it would be much easier to buy a Garmin 2820 with BlueTooth than change out all my other hardware for 2 motorcycles.

Or I saw a mention on a "dongle", still not quite sure what this is??

I would like to get a bluetooth communication system, looking at the Sena SMH10, so I could be listening to my BlueTooth from the GPS also.