Has your iPhone recently been not ringing it’s manually set alarm in the morning.
This is a bug in the iPhone operating system iOS. The workaround is to set a recurring alarm.
According to 9to5mac, this is a temporary problem, until 3rd January 2011.
So better inform whoever owns an iphone to set an recurring alarm and not a onetime alarm or the alarm will NOT go off!
Visit Apple Singapore's website www.apple.com/sg.