I still use one which gets one-way service from <https://pagersdirect.net/> (~$14/mo, with phone number and pager included). Most US cities, large and small, still have active infrastructure. I live in a city with a few hundred thousand people, great coverage.
This has replaced my mobile phone, which I no longer carry. It also prevents spammers from messaging... because the systems don't understand this antiquated technology [1].
For those interested, Pagers Direct has an email-to-pager option (I don't use it, phone digits only please caller, after the beep). It also has two-way pagers, which I have no experience with.
One caution: for one-way pagers, if you're out of range[0] when somebody sends you text, you will never get the message (no handshake/confirmation).
[0] does not use traditional cellular infrastructure
[1] TBH: most humans don't either, unless you explain how to page somebody: key in your callback#/code after the beep [no audio/text]
[•] I don't work for the above-linked paging service, I'm just a very happy customer.