A free program for Android, by Just Call Apps.

Are you the type of person who loves pranking your family or friends? Is this the way you want to put smiles on their faces? If so, then the Call Voice Changer app is just for you!

As you perform a call, you may change your voice to various sounds. May it be the voice of a man, Santa, squirrel, alien, penguin, etc. To be certain of what sound to choose before making a call, there is a Test option wherein you can hear what a voice sounds like.

This awesome app can be downloaded on the Google Play store.