Hi, I recently did something similar but with a Nokia.

They sell a cheap car kit which is basically the incar version of a wall wart - It plugs into the cigarette lighter and gives you a power and audio out speaker from the phone. The sound quality is poor but when teamed up with an impedance maching unit from CPC (around £7), it can be linked directly to my front amp in parallel with the empeg. Because the impedance matcher is isolated from the car phone, you get no noise whatsoever when the phone is not doing anything but it sounds crystal clear when the phone rings or you are talking.

Team this little lot up with a thing called a GISMO from www.innovations.co.uk (£15) and you have an almost full solution. The gismo will listen for any valid GSM carrier wave in the car and, when connected to the empeg mute line, will mute the empeg with your desired mute setting. I use a 50% volume reduction.

I have hidden all of this in the dash and just have the phone holder/connector visible. Works a treat.