If your phone is not frozen, you can turn on "digital" versions of your hardware keys (without erasing network settings as mentioned above). Go to settings > general > accessibility > assistive touch > "on". A small white dot will show up on your screen, which you can move wherever you'd like to keep it. Tap the dot, tap device, and there is your lock screen, which if you hold down will bring up the power off red arrow. You can use these buttons the same way you would the "real" button.