Nokia E51 and GPS Bluetooth

Hi

Just got a Garmin 265W with bluetooth.
When i take an incoming call through the GPS i can't hear anything.Only way i can change this is if i pick up my mobile while its ringing and hit options and change from handset to bluetooth which kind of defeats the purpose.

Is there anyway i can have it come straight through to the gps?
It works on the first call after pairing but after that goes back to handset.

Any help would be good thanks!