Originally Posted by RocketMoto
There are lots of these around...
Take a look on eBay for the Jabra A210S (be sure to get the "S" stereo version). You can typically pick one of these up for short money. Honestly, nearly any A2DP 'dongle' will do what you want. The only downside is having to recharge yet another battery.
Careful here - I think the Jabra A210S has a 2.5mm lead, which will not be compatible with the 3.5mm Audio Out from the Zumo 550, although an 2.5-3.5mm converter could be used, but that would be clunky on the side of the Zumo cradle. Jabra's older A120 had a 3.5mm jack, if you can find one.
As a temporary measure, I have bought the Sony TMR-BT10 for £4.99 (!), even though it has a useless charging base, but fine for day use. Comes with a 3.5mm jack. Stop gap measure until Sena bring out their own Bluetooth Audio Gateway, which hopefully will have a bike charging option and is weatherproof.
Hope this helps.