Well I really would have like to use my car's existing prewiring for the speakerphone, or atleast some of it, but could not.
I bought the $200 SprintPCS speakerphone for my 8500 and had it installed. Mic is above the visor, speaker is in the passenger footwell, and phone is mounted on the passenger side of the console. Installation costed me $120.
Overall, I love having a speakerphone and am happy with the setup. I tried wiring a second wire from the speakerphone speaker in the foot well to the existing in car speaker in the rear trunk lid. The ohms were rated differently, so the output is very minimal... oh well...
Also, I do not like the phone mounted in the car and where it is. It was the only place, so I guess I have to live with it. And it's very functional, but I don't like how it has to be drilled. I just wish there was a secre place it could go. But then again, I need it to be somewhere close by and within visibality to dial, etc.
I guess you can't have it all!
Overall, I love it though! I love not having to hold the stupid phone, can speak freely! ANd works great with voice-dialing!
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)