What Iphone application can I use to use as a supstitute for a microphone for ventrilo?

My microphone on the computer is broken, what Iphone (3G) application can I use to replace a microphone?|||There is an app called "Megaphone". It is free and you can download it from AppStore. Connect the headphone output of the iPhone, to the Mic input of your PC and.... ready!!! :)