Google to ditch SMS support in Hangouts for Android effective May 22
However, this time Google has decided to ditch one of the features that made Hangouts a multipurpose messaging app. Although Google has yet to confirm the information, it appears that SMS support will be removed from Hangouts for Android.
Last year, we announced several improvements to the most popular features of Google Hangouts, such as the new video meetings experience and better group chat messaging. As part of that ongoing effort, we will be removing carrier SMS text messaging from Hangouts on Android after May 22, 2017.
It appears though that Google Voice numbers will continue to be supported after May 22, as the change will only affect SMS messages sent and received from carrier phone numbers.
Starting March 27, Hangouts users on Android will be prompted to choose another default messaging application that's already installed on their smartphones. If none are available, then they will be immediately redirected to Google Play store to find another SMS messaging app they can use.
source: Reddit via AndroidPolice
Things that are NOT allowed: