What has happened to the ATC voices?

The voices are gone because there was a hotfix on the app due to frequent app crashes because of ATC voice glitches. Unfortunately, with this because of problems beyond infinite flight’s control. With this hotfix, voices were removed. The problem was that some of the voices were not working true to a problem with Apple’s test to speech system. Apple is working to fix it, however Infinite Flight is going to do all they can to get the voices back once they feel that Apple systems with voices are running again.

More information to be found in the article I linked below