When you've used telnet, the device on the other end was running a telnet server (though usually referred to as a daemon at least in *nix systems). You were using the client.
Telnet was once the dominant method of CLI access, but has largely been deprecated to SSH since telnet is an inherently insecure protocol (credentials are sent cleartext). So we also have an SSH server (with the cute name of "dropbear", and so you may see event log entries with that mentioned) to provide secure CLI access. An example of an SSH client is PUTTY which we often refer people to.
We've had telnet (and I think it's still an option to enable it) since our first products, but you generally should not enable it.