If its the Same Simcard Same Network, but just a Software Update, then it is apple software issue. the only real thing i could see is try to hard update it again from a PC/Mac using itunes, and if that doesn't work bring it into your service provider. Make sure you have a backup of all your stuff before continuing ! ! To put the phone into hard reset mode plug it into PC/Mac then hold the power and home button, when your phone powers off and you see the apple logo pop on, let go of the power button but keep holding the home button. now itunes will say it needs to be restored.
You might have pressure on the screen somewhere, take the phone appart and than re assemble it to make sure that all the parts are sitting flush. any part off with cause other parts to not sit right in the phone.
I Would Suggest not taking it out after a few hours, let it sit for a day or two, to ensure that all the water has been pulled out of the phone. You don't want to Turn it on prematurely to have it short components.