how to reboot your phone if the power button is broken

To ComputerFixer - THANK YOU THANK YOU THANK YOU!!!! I've spent the last 2 hours SO frustrated w/ this stupid iPhone! My iPod 4 is too old and I cannot afford to buy a new one due to paying for new computers and iPods for our girls for college... so my husband gave me his old iPhone 4. I cannot use it as a phone and the top button doesn't work, but other than that it is MUCH faster and has a more up-to-date OS than my iPod does. I have to use the Assisted Touch in order to lock the screen, so I already knew that existed. HOWEVER, today I tried to update what I am now calling my PhonePod (the iPhone 4 using it as an iPod) and it WOULD.NOT.WORK.... I had the feeling something was getting hung, but could NOT figure out how to restart the stupid thing. My husband took over for me and found your reply above about using the Assisted Touch and holding the Lock Screen icon down, and IT WORKED! THANK YOU!!!!!