From Christian Lheureux:

If not already done, configure the SERVICES.NET.SYS file. If the file does not exist, a sample can be copied from SERVSAMP.NET.SYS. Then link this file from posix space under the name /etc/services.

If not already done, configure the PROTOCOL.NET.SYS file. If the file does not exist, a sample can be copied from PROTSAMP.NET.SYS. Then link this file from posix space under the name /etc/protocols.

If you wish to enable security features (allow this ip, disallow that one, e.g.), you will also need file INETDSEC.NET.SYS and its link /usr/adm/inetd.sec.

You will also need file INETDCNF.NET.SYS (can be copied from sample INCNFSMP.NET.SYS) and its link from posix space /etc/inetd.conf.

All these files are more or less self-documenting. They're basically ASCII files that you can modify with the editor of your choice. Then you start job JINETD.NET.SYS. Telnet is one of the internal facilities of the INETD daemon launched by this job. This should do it.