The PolyTune for iPhone App is not working correctly. Any ideas?
First, it will work with the built in mic if the signal is loud enough, and you should be aware that not all guitars have sufficient acoustic output so that the iPhone's built in microphone can pick it up
Second, it would seem that the microphone on the original iPhones are not as sensitive as the ones on the 3G and 3GS models.
For electric guitar we can recommend using a cable such as the Peterson iPhone / iPod cable or the IK Multimedia iRig plug interface adapter.