This means that if you have a phone running BlackBerry 10 or BlackBerry 7.1 OS or earlier, then as of January 4, 2022 it will no longer reliably support: Phone calls; SMS; and 9-1-1 emergency calls.
BlackBerry says WiFi and mobile data might also become unreliable, and applications including BlackBerry Link, BlackBerry Desktop Manager, BlackBerry World, BlackBerry Protect, BlackBerry Messenger, and BlackBerry Blend "will also have limited functionality."
The BlackBerry PlayBook tablet is also reaching end-of-life status, which means that anyone hanging onto the 10-year-old tablet will also find it severely limited starting 4 January. We are not sure how you would tell given that a decade old tablet would normally be a bit slow anyway. However, BlackBerry discontinued the tablet a year after launch suggests that there probably never were all that many PlayBook owners in the first place.
Folks who are still using a device with BlackBerry OS will want to check out the company's FAQ for tips on migrating their data to other platforms while they still can.