It doesn’t need a data plan like the ones you or I buy. There are a lot of services that buy bulk open data services from telcos. And they’ll just keep having data access as long as the modem is still supported.

My CPAP has a 2G cellular modem in it and it was sending my usage data to my doc (and probably others) every morning for years until the last 2G supporting cell tower in my area was shut down.