Yes you can not telnet directly to the server as far as I know. You can however run the tomenet client on a remote Linux machine (such as a shared server) and connect to the server that way. There might be free servers you can run the TomeNET client off of. That of course may add some lag. I think the server is in France, so know that before you sign up for a VPS on the other side of the planet in Japan.

In the guide there are instructions on compiling the client. You can compile a client with only one window for telnet use. You can set the number of windows to one, before compiling the client. Then I think it should work via telnet if you have a remote machine that can run the client via telnet.
Michael or Blue can definitively say if the client can run on a remote host via telnet and not try to open a new X session window and instead start in the current CLI session.