Here the steps for being able to activate the telnet service on a freebsd server:
execute /usr/sbin/sysinstall, then select the voice Configure - I give post-install configuration of FreeBSD, then select the voice Networking - Configure additional network services then select the voice inetd This machine wants to run the inetd daemon, always answer yes to the all questions and finally unremark the line with telnet stream tcp nowait..... and press esc and two times shift+z to save changes.
Once let out that from the masks of the sysinstall and executing: /etc/rc.d/inetd restart as root user.