Hoping you can help. I have a 1 month year old 7. Yesterday, out of nowhere, my microphone stopped working. I can hear fine but no-one can hear me. No drops. Didn't get it wet.
Can they hear you on speakerphone, or with a wired or Bluetooth headset? If that's the case, then check the primary mic opening to make sure it's not blocked or clogged by lint. Also, see if it happens in Safe Mode: https://support.t-mobile.com/docs/DOC-40134
If you do think you're going to send it in, then do a factory reset yourself first to see if that helps. Might save you from having to go through all the trouble of sending it in.