Convert 2001 7 series in-car cell to iPhone

Please help. What is the most economical way to change my motorola cell phone in my 2001 740IL to my 3G iPhone. Thanks

I found using a Jupiter Jack works great. I bought it for $10.00! You can go to https:\\jupiterjack.com for a demo. You plug it into your cellphone, dial 99.3 FM on the radio (program this in for easy access) and it turns your phone into a speaker phone going thru the speakers in your car. It works just fine.