Apple get a life
Sometimes my iphone 5 does not turn up or down sound and the multitaskiing doesnt even offer the sound when that happens
Try the usual steps: restart, reset, restore.
http://support.apple.com/kb/HT1430
http://support.apple.com/kb/HT1414
If you try restoring from a backup and that doesn't fix the problem, try restoring to factory settings and, if the problem goes away, then synching your apps. You'll lose the app data and settings, but if the problem is due to a corrupt cache or settings file, that should cure it.
If none of that helps, your device may have developed a hardware fault and will need to be take or sent to Apple.
Regards.