iphone can't open i forget apple id

Have you tried : If you forgot your Apple ID - Apple Support ?

Or, and if you bought the phone new (i.e. it’s not second-hand), you could try going to an Apple Store (make a Genius Bar appointment if you do) or try contacting iTunes Support online (http://www.apple.com/support/itunes/ww) and see if they can remove the phone from the account - they are likely to want to see proof of ownership before they might help e.g. original receipt with the serial number on it