Some users of Apple products are reporting that the “Do Not Disturb” function is not turning off. This means that all calls go straight to voicemail and text messages are silent.

The problem seems to effect iOS 6 native devices, include iPhone 5, fourth generation iPad or iPad mini starting on January 1. Apple indicates that the solution to this matter will simply appear on January 7, suggesting some internal OS error dealing with the change over to the next year.

Source: Support.Apple.com