If you have SSH I can't think of a reason you'd need telnet. If you're on the stock Pogoplug OS you can enable telnet by doing the following:
mount -o remount,rw /
vi /etc/init.d/rcS
Find the part that looks like this:
if [ "x$cedebug" != "x" ]; then
telnetd
/usr/sbin/dropbear
fi
and either delete the if and fi lines or comment them out.
Your rcS file may look a little different.