hands free through car stereo

[sixto]

I'm looking for a hands free kit that doesn't require a headset or ear bud. Is there a device that uses the common 2.5mm jack found in just about any phone except Nokia and Ericsson? I saw something that clips to the receiver and broadcasts over FM but it doesn't look like it's worth money.

Ideally I'd like to hook up my phone to the factory phone connections in the S420. I'll gut the phone if necessary.

Any recommendations or advice out there?

Thanks,
Sixto
95 S420
87 300SDL