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Look into FM transmitters if your HHR doesn't have the 1/8 jack in the front. My 09 does and I just use a short male to male cable from Radio Shack sorry its now call The Source.
I use my cell phone as a stereo with a mini RCA jack plugged into the headphone jack of the phone, into the auxillary input on front of HHR stereo. You can't really "integrate" unless you use an Ipod.
I suggest fm transmitter as well. I will say I have an after market head unit with blue tooth stereo and I can stream music from my Evo which is pretty nice.