Sony Ecricsson P900

Can any one help me please I have just installed a car radio with Bluetooth
I can pair my P900 with it ok but do not work when I get a call or if I
press the talk button, I have paired my wife's Sony Ecricsson K700i and it
works fine with it, so is it the Bluetooth software on the P900.
The software on P900 is CDA162003/5 R5A07 and Bluetooth software is CXC12529
R5D if this helps

Thanks for any help!