If you've installed AppSync (if you jailbreak) pressing double click and you get into the itunes, syncing, and passes it to you phone. Another way is to have ifunbox, if you have this program you open it and in the left menu select Installous App Install and in the top menu select the Copy from PC option, choose ipa that you have and what you get into this folder in Iphone. Then you have to do is open the Install0us, go to Downloads, select the ipa you've got to give ifunbox and install