Apple has somewhat acknowledged an issue with the microphone on iPhone 7 models running iOS 11.3 and later. It’s entirely unclear what the cause happens to be, but the effect is that the speaker button appears greyed out during calls; while some users may not be heard during FaceTime chats and phone calls.
The company informed its Apple Authorised Service Providers of the issue through an internal communication. The memo instructs providers to make this issue an exception for those bringing in iPhones that are out of warranty; allowing them to fix it without a service charge.
As far as problems go, this one doesn’t appear to be very widespread. Affecting only a handful of devices. However, there have been several documented cases of Apple users complaining about the issue; which is likely to have prompted this action from Cupertino.
Still, nobody is entirely sure what is causing the microphone to become disabled. One theory is that the software update is causing a hardware malfunction, since the language in the memo indicates that the devices may require repair.