yes , you can install youtube but it is not original youtube from google but you can use youtube alternative for iphone 4 by jonas gesnner its called protube . for installing protube; 1)you need jailbroken iphone 4 . 2)open cydia sources , click on edit , add ,copy paste following repo; REPO: http://cydia.kiiimo.org/ 3)after adding repo click on search and find protube and install it . 4)after installing you can find protube in home screen on your iphone . 5)launch protube you can now use youtube in your iphone 4 . 6)enjoy!!!