In addition to telnetd, BeOS has the ability to accept logins via the serial port.
Connect any serial terminal to your BeOS box’s serial1 with a null-modem cable. Set your terminal speed 19200bps. Type at the BeOS prompt

$ getty serial1 19200 &

then hit Enter at your serial terminal. You will see the login prompt:

(hostname) login:

Type your user name and password to log in.