Why doesn't my iPhone 4 ring when it is in sleep mode?

[iMore Question]

iPhone 4 - Phone doesn't ring when it is in sleep mode

I am using my daughter's old iPhone 4 after it has been unlocked by AT&T. Everything works fine except the incoming calls go straight to the voicemail box when the phone is in sleep mode. Neither sound nor vibration with incoming calls in sleep mode.

 

[alicepattinson]

Re: iPhone 4 - Phone doesn't ring when it is in sleep mode

Still in what iOS version your iPhone 4? Try update it to latest iOS version that is compatible with your iPhone 4.