Messenger signups without a Facebook account are no longer possible | Engadget
You'll no longer be able to sign up for Messenger if you don't have a Facebook account. Back in 2015, the social network started allowing potential users to sign up for its messaging app using only their phone numbers. Now, an entry in the website's Help Center clearly states that "you'll need to create a Facebook account to use Messenger." The company has also confirmed the change to VentureBeat, telling the publication that "the vast majority of people who use Messenger already log in through Facebook" and that it merely wants to simplify the process.
Dec 27, 2019 ... Messenger signups without a Facebook account are no longer possible ... already using the app without an account don't need to do anything.