iOS 11.3 Update Crippled Microphones On Some iPhone 7 Units According To Leaked Apple Doc

An internal Apple document appears to confirm another issue that has popped up with iOS 11.3 and pertains to the iPhone 7 and iPhone 7 Plus smartphones. On those devices, the update has created a microphone issue on what Apple says is a limited number of devices. Affected users may see a grayed-out speaker button during phone calls. The issue can also prevent some users of affected devices from being heard during phone calls and FaceTime video chats.

An internal document cited by MacRumors has instructed Apple Authorized Service Providers to ask customers to disconnect or power off any Bluetooth headsets or audio accessories connected to the smartphone and see if that fixes the issue. If the speaker button is still grayed out for calls, the service people are to run audio diagnostics.

If the smartphone is affected by the issue, the diagnostic tools will show "device could not detect dock" or "accessory not supported". If either of those messages is seen, the service provider can initiate a repair. For devices no longer covered under warranty, the service provider will be able to initiate an exception for the issue. Apple hasn't stated specifically what is causing this issue, but it seems that the software update is causing some sort of hardware problem.
When Apple first started to talk up the iOS 11.3 update there was a lot in it that folks were excited about. This is the update that was to bring with it better battery health information so that iPhone users could tell if their device was being throttled. That was a good thing, but when the update landed it was quickly discovered that it was also bricking iPhone 8 devices that had third-party screen repairs by disabling touch functionality. Apple later promised that it would roll back that change with iOS 11.3.1.