I have the same problem with my iPhone 4! It literally had no issues until a few days after the iOS 6 update. Now I only have volume when someone calls me. I have no volume for videos that are on my phone or online. My keypad doesn't click and there's no sound when I send or receive a text. Only phone calls actually have an alert tone. I tried resetting my phone by holding the circle and power buttons and that didn't help. I've gone into my settings and tried turning on airplane mode but that did nothing too. I'm getting so annoyed!