My iPhone 3G freezes on its own and stays that way for several hours. During this time I cannot turn off my phone and the touch screen is unresponsive. I also cannot recieve texts or phone calls. On whichever screen it decides to get stuck on it has a little circle in the center as if it is thinking. After about six hours it unfreezes on its own but I can only use it for a minute or two before it freezes again. I have tried plugging it into iTunes and nothing changed.