Apple iOS 12.3.1 update released to fix iMessage and VoLTE issues0
As far as the contents of the update go, Apple says that iOS 12.3.1, which was released just two weeks after iOS 12.3, addresses an issue that could prevent iPhone users from making or receiving VoLTE (voice over LTE) calls.
Also, the update fixes many of the problems in the Messages app, including those that could cause messages from unknown senders to pop up in one's conversation list even though the Filter Unknown Senders option is enabled.
Another Messages fix should solve another bug with Messages, which could prevent the Report Junk link from appearing in the app's threads from unknown senders.
In other news, Apple is gearing up for the next major iOS 13 update, and you can already read about some of the changes that will be implemented here. Keep in mind though that Apple hasn't yet confirmed anything about iOS 13, so take it with a tint of salt until the update is announced.