Does anyone know how to get ped the p code to unlock an iphone?

I loaned a friend some money and he gave me his Iphone as collateral and now he cant pay me back so I'm keeping his Iphone. I gave him more than enough time to pay and now the Iphone is mine but I cant break his p code and of course he refuses to give it to me. Can someone help me. I tried to link to Itunes but I still need the p code so no luck there. I'm open to suggestions.