My iPhone model is a 3G, about 5.5 years old now and the tech is likely older and I'm attempting to keep it "going" forever. I've overcome many issues with it, but it reached the point where I could not turn it off. Being a "limo driver", this really was not an issue because I never turned it "off" because I am always available to my customers. But, lately, I've switched to "Pure Talk" (this is NOT an advert, but the service is great!) and I added some services which directed me to reboot my iPhone 3G. So Here's what I did with success: I lightly moistened a cotton ball with regular rubbing alcohol and then gently passed it over the on/off button (upper right top) several times so that there was some minimal penetration into whatever was below and might have needed cleansing. Then I used a can of compressed air to blow into the button...liberally. Finally, I squeezed the upper right corner of the iPhone while simultaneously pressing the on/off button (as suggested herein), and voila !!! it worked !!! Thanks to all for your suggestions. Hope this adds something to the discovery process !!