iPhones, like computers, need to be rebooted on occasion. Maybe iMessage is acting up, for example. If your Home and Power button don't work, though, rebooting can be tricky -- but you can still reboot your Phone by changing some settings.
OS X Daily explains that changing certain settings will cause the phone to automatically reboot. For example:
- Changing the Accessibility options to Bold text
- Resetting Network Settings (note you'll lose saved passwords)
The Accessibility option is obviously the first port of call, since it won't erase your saved passwords -- but it's good to have both options.