https://techcrunch.com/2019/07/22/apple-fixes-walkie-talkie-app-vulnerability-in-watchos-update/

If you are, for some reason, an avid Walkie Talkie user on the Apple Watch, you will be pleased to learn that the functionality is back in the latest watchOS update today. The watchOS 5.3 release notes specify that the update “[p]rovides important security updates including a fix for the Walkie-Talkie app.”

The feature was notably disabled nearly two weeks ago after Apple discovered a vulnerability, one which was unspecified but was clearly serious enough for them to quickly pull one of the hallmark updates of watchOS 5.