The thing is that I know fOr a fact that in this particular group of people everyone has free SMS and/or iMessage. Moreover, they all know rah others' real names and phone numbers. Some talk on the phone, yet use Facebook for messages. These are not people who care about federation. It's just some kind of bizarre force of habit.
These are also all the people who have at least a thousand unread emails in their inboxes. I know one person who has roughly 60k unread emails dating back to 1997 when she created her AOL account. She is not a Luddite and very good at using other types of tech but somehow never mastered email.