you do realise how bad an idea this is? You really should use ssh instead (which is probably already running and ready to go...)
redhat-config-services is a command from Redhat EL3 and earlier, if you aren't using that, it's the wrong command. On newer Redhat, CentOS or Fedora systems it's called system-config-services, and you don't want the ./ bit at all. Learn about that another day. In future, please always ensure you tell us what version of linux you are using, etc.
Generally on most systems you can do this... open /etc/xinetd.d/telnet in a text editor as root and change the line that says "disabled = yes" to "disabled = no". then you need to restart the xinetd service by "service xinetd restart" or "/etc/init.d/xinetd restart" and that should be it. This depends on the telnet server being installed in the first place, of course, which these days it won't be.
if you're using debian or similar then you might still be using inetd, not xinetd, in which case youd' do an equivalent edit of /etc/inetd.conf.
Again though, telnet is BAD. SSH is GOOD.