It is not recommended. Everyone should use SSH as it is secure. Telenet is not, and anyone monitoring your network traffic could grab your login/password. With that warning aside, sometimes you may have to use Telnet. To do that you need to do the following:
#telnet stream tcp nowait root /usr/libexec/tcpd telnetd... by removing the # symbol at the start of the line.
root 410 0.0 0.0 1308 44 ?? Ss Wed01AM 0:00.00 inetd... then type sudo kill -9 410, where 410 is the PID as shown in the output above. Then run inetd again with the command sudo inetd. You could do this all at once by typing sudo kill -9 410; sudo inetd
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030818084455459