It still is popular, even if only RAI has it this days. My dad still uses it, and you can access teletext even on new televisions/decoders.
It used to run on VAX hardware long, long ago... now it's all VMware on the servers.
In the '90s they had 'interactive teletext' services, like a few banks did, where you would phone in, get assigned a teletext page, and use it as your screen while interacting with DTMF: teletext 'apps'.
Those where the Red Hat 5 days and there was a system that would fax error reports to the other room :D
PS: some of the live captioning you can see around runs on Erlang too.