You don't need a carnet to buy a pre-pago chip, but you do need one to get a post-pago plan or to buy a phone. I don't have my carnet (yet, it's in the works!), but my boyfriend helped me buy a phone and his friend took out another phone line which I'm using.
Cuyguy, I hope you found a phone. I might have something if you still need it, otherwise... there's a huge amount of "informality" in Peru and you can definitely get a phone through those channels. I don't condone it, but it seems to be a way of life here.