This will only work with car stereos that have aux 3.5mm stereo input. Use a 3.5mm to 3.5mm stereo cable and plug it in to a 2.5mm to a 3.5mm stereo adapter. Plug it in about halfway. Plug the 2.5mm end into your phones headset jack. Plug the other end of the 3.5mm to the aux input of your car stereo. Set your car stereo to AUX. make a call to *2 or popcorn and move the 3.5mm stereo cable thats plugged into the 2.5 adapter in and out of the adapter until you hear the call come through your car speakers. Once you determine the right position you can secure the connection with a piece of tape so it doesnt move. Now hang up the call. Now make a new call to *2 and use its voice command to see if your voice can be recognized. Or you can call a friend and ask them if they can hear you. If you do this correctly your friend should be able to hear you and you will hear them through your stereo.

For my setup I've also purchased a dashboard mount from Best Buy for $14.99. I've also signed up for Voice Command from Sprint and it works quite well with this setup.

Total cost less than $20.