Hands free calls for free on factory stereo

I just changed my phone to the my touch from Tmobile. I have a prius II and it only has the audio in for the factory stereo. I connected the phone to listen to some music through pandora when I got a call from a friend. The music stopped and the speakers now was streaming my friends voice over the speakers. This was the best free idea that just came about. You can just speak normally (at least on my phone) and he could hear me just fine without echoing. This was better than bluetooth and better that using a hands free set. Hope everyone enjoys.