Unless you have a factory head unit with a built in BluTooth you'll need to do an add on.
I hear great things about the Parrot stuff.
I got a great deal via ebay on a
Motorola HF850 so I went with that. Well worth the $49. I paid for it.
I didn't try to jack into my stereo, the speaker that comes with it is plenty loud, I just have it sitting under the passenger's seat. For as little as I use it, it works fine for me. Very easy, clean install in the 4Runner.