Depends on how old you are and where you live. As a college student in North America, everyone uses Messenger, nothing else. How would leaving Messenger work without shrinking your social circle to 0? In other countries, like where my family lives for example, no one uses Messenger or has heard of it — everyone is on Whatsapp. So depends on your demographics.

I'm a college student in North America and I don't use Messenger.

Coincidentally, my social circle is approximately 0. It has never previously occured to me that this may not actually be a coincidence.

I assume these college students are using messenger via their cell phones, correct?

Is it no longer possible to reach people via text or phone?

Nope, cell phones are the most popular method, but there's also a web app for Messenger (messenger.com) which makes it even more convenient.

I'm not even quite sure what Messenger is.