time2focus, you got very close, so I'll have to reveal the idea.
He is using a gadget that helps him to control his voice. But it's not exactly a computer program from where he controls his voice... it's an application at his iPhone. There's an equalizer that he tunes. Imagine this - he needs to change his voice to rap? No problem! He pulls out his iPhone and gives himself the voice exactly as he wants by playing with the equalizer.
At the bottom line, it's a cheating. The protagonist himself has a very childish voice. That's why he was rejected by many producers... Until he got the device.
Now about the gadget. Today's technologies have
Artificial Vocal Cords. So I decided to take that concept a little further. In my story, it's a small gadget that can be simply inserted into the mouth and filter the voice accordingly to the presets in the application. The user can sing and talk in that voice, but there is one obstacle - as long as the gadget is working, it eats the phone battery VERY FAST. There are times in the story, where the protagonist almost gets busted because his iPhone runs out of battery.
P.S. Maybe it's a little bit Science Fiction story