my iPhone 5s doesn't ring or give text alerts every time

Additional info: My provider is AT&T. The problem has occurred in multiple locations with varying signal strengths.

I think we do in fact have a similar problem. When my phone is in sleep mode is when it doesn't always produce phone rings and never gives text alerts. I just verified this by having my assistant call and text me from her Verizon Galaxy phone and call me from our office land line. From sleep mode my iPhone didn't ring with the first phone call from her cell or her first text message, but the text message did arrive. She said my phone went straight to voicemail on the call and the text showed as delivered. The land line test call did ring my iPhone. A second attempt to call my sleeping iPhone from her cell phone did result in my phone ringing. A second text attempt had the same result as the first, no alert, but the text did arrive. A third text attempt with my phone not in sleep mode resulted in a text alert with the arrival of the text. I did the same test, calling and texting my phone, with another iPhone 5s. My phone rang from sleep mode but didn't give a text alert.

So, it would seem that this is mostly a text alert issue only when the phone is in sleep mode. I'm going to review all my settings and failing finding something there that solves the problem I may call AT&T (if I am feeling patient). I'll report back if I find a solution.

Thank you jtfey. I never knew what that button was. I've only used that pull-up screen to turn on the flashlight. I must have accidentally hit the DND button while using the flashlight and not realized it. To bad that you had to make a trip to AT&T to find that out.