Personally, I would not use telnet at all. Anyway, here is an extended HOW-TO that builds on top of what Laura V. has done. All the credit should really goes to her. I just added a few step before and one minor change on the second to the last step to complete the HOW-TO.
0. Download and burn the DVD ISO from here.
1. Copy the following two files to the target machine.
scp [DVDROM]/Solaris_9/Tools/Boot/usr/sbin/inetd [USER]@[HOST]:/usr/sbin/inetd.s9 scp [DVDROM]/Solaris_9/Tools/Boot/usr/sbin/in.telnetd [USER]@[HOST]:/usr/sbin/in.telnetd.s9
2. Disable telnet in Soaris 10
svcadm disable svc:/network/telnet svcadm disable svc:/network/inetd
/etc/inetd.conf.s9 file with the following content:
telnet stream tcp6 nowait root /usr/sbin/in.telnetd.s9 in.telnetd.s9
4. Start Solaris 9 version of telnet with the following command
/usr/sbin/inetd.s9 -s /etc/inetd.conf.s9
5. Double check if you can telnet from a different machine.