wrote:

They sell some sort of device that you plug a portable MP3 into it,
and that thing sends the music to a blank radio frequency so the mp3
player can be heard on the car radio.

What are these things called?

FM modulators [$10-20] plug into your cigg. lighter and send a signal
to your radio. If you're in a rural area they work OK. Not so
much where there are lots of stations and radio interference.

Auxiliary input adapters [$30-100] need to be powered, and you need to
pull the radio far enough to plug into the antenna in the back. They
work much better, IME.
http://www.amazon.com/gp/product/B00...00_i00_details

If I didn't have a 2001 Impala that needed the factory radio for a
bunch of stuff, I'd have bought a $40 stereo with a phono plug.
[on my Impala you need to buy a $100 cable and route it to your trunk
so the factory radio can continue to do whatever it does]

Jim