I use mine all the time. I used to use the tape adapter till I got a stereo upgrade. Now I use the male to male auxilary cord. Plugs in and you can listen to music and when you get a call it stops the music and let's you take the call through the speakers then when they hang up the music resumes.
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I have an aftermarket JVC stereo in my car. It has a 3.5 mm aux jack. I use a 3.5 to 3.5 patch cord, choose the aux setting, and fire away. I also plug it into charger. Busy with wires, but it works.
If you're going with an aftermarket unit, bluetooth is a must. plenty offer it for under $100. You can stream anything wirelessly so its pretty convenient. I also like using poweramp because it starts playing my music as soon as a connection is made. My phone can remain in my pocket and my 10gigs of music are already playing