iPhone won't connect to UHP Bluetooth hands-free system in Vectra

Just bought an Apple iPhone and delighted with it. Unfortunately, I cannot get it to work with my Vauxhall Vectra UHP Bluetooth System installed in my car. I can get the iphone to pair up with the car, but it only connects momentarily before disconnecting. My previous handset (Blackberry 8120) worked a treat?
Can I download some sort of patch or driver to cure the problem? or am I just doing it wrong?
Advice greatly appreciated!
Nick Brazier