This is really simple, and you probably already tried this, but I have found that with the 755p and some in-car bluetooth, that I have to actively tell the Treo to connect to the vehicle initially. (Go to bluetooth > setup devices > trusted devices > highlight the vehicle's bluetooth(after pairing) > press 'menu' > choose "connect")

Worked for me in a Range Rover that otherwise connected without this step with my 650, and a friends 700p.