September 26, 2012: Installed a cheap and simple speaker system for my iPhoneI've been using headphones (yes I know it's illegal) to listen to the King James Bible, music, talk radio, and football games on my iPhone while driving to and from San Jose every weekend.
I've been wanting to connect my iPhone to some speakers but I've been very busy... I finally got it done!
What I've got is an 88watt speaker driver and a 10" compact subwoofer with a built in amp. Then I am using a 3.5mm head phone jack split into two RCA connections for both amps.
The 88watt speaker driver runs my four interior factory speakers (split by right and left channel, but without a deck there is no ability to fade from front/rear), and the subwoofer is self-powered.
The total cost for all of this was under $100! The woofer was $90 on Amazon with free shipping and the 88w amp I got for free from my friend Brandon (it's verrrry old, I think made in 2001).
The system works GREAT! I have a simple male 3.5mm headphone cable that runs out from my center console and simply plugs into my iPhone - or any other device with a standard headphone output jack. The bass on the subwoofer is adjustable and the system really kicks!! It's the best system I've ever had in my car and it was super cheap!!
Now driving long distances is great! I can listen to music and anything else without needing head phones. It's been just great.
Also, the headphone cable neatly tucks away from view when the car is parked, and everything is hidden and out of view -- the stock radio bay is empty with partially chewed up speaker wire remains from the squirrels and mice during the car's six year unprotected Coarsegold foothill hiatus.
Only a $90 system

Unfortunately the woofer is a bit too tall to fit below the seat. I could have gotten an 8" unit for $10 less, but I thought for $10 I might as well get the larger unit.