I've been doing some reasearch on this topic and found that you can in fact use your Blackberry as an MP3 player if your car has an auxiliary input. I was wondering if anyone has experimented with using this feature to make/receive calls? Would I be able to connect my Blackberry via an aux cable to my car and have the functionality of handsfree calling (like Bluetooth) for calls?

Doubtful.
The Aux is usually just an input... not an output.
You'd not have any microphone capabilities.

Any other suggestions to get something like this to work? It's an 07 ford and is a year shy of having microsoft sync.

You could use your Blackberry for a handsfree unit.
Plug in the Aux input to the car and to the headphone jack on the phone.
Turn on headset mode when you answer the phone. The audio will be through your speakers, and input through the mic on the phone. Not sure if this would give any feedback, though.

Wirelessly posted (BlackBerry Curve 8900)

I actually do this all the time. When listening to music and someone calls, the music stops playing and I answer the call. I press the speakerphone button and then I can hear them over the car speakers. They can hear me via the microphone.

Jeremy,

I cannot get this to work like you can. When I plug in an audio cable to my Blackberry, it recognizes it as a headset. Therefore, when I answer the phone switching to speakerphone is not an option. I can switch to headset where I can then hear the caller over my car's speakers, but they cannot hear me. I can switch back to handset and hear the caller and talk back to them. Any suggestions?

Sounds like you'll need a BT speakerphone kit then.

If you have a USB input on your stereo, you can play the music on your ipod right off the phone. Just plug the USB cable you use on your PC and connect it that way.