IP Messenger is one of the most commonly used lan chat options in corporates if you don’t have any other means of communication. It is less of distraction and features which are just required for you to talk.
We wrote about IP Messenger[ Chat on Lan with IP Messenger ] here and one of the most commonly question asked was How do you run it on different port number ? By default IP messenger determines a port and finds other instances of IP messenger running on other computers to bring everybody together.
However there is no direct option to set a port number but if you do want to, One of our reader, Sriram has commented :
Short Description :
Invoke IP messenger.exe from command line like this C:> IPmessenger.exe [portnumber] . This opens another instance of IP messenger along the one which is running already. However you can talk only to people who are also running it on the same port number. This is the key.
Long Description :
I tried to re-collect it a lot and found the way. It is very simple.  Download the latest copy of IP Messenger from http://www.ipmsg.org/index.html.en (you might know this).
 Extract the zip content provided by.
 There is a direct ipmsg.exe file which generally we use. Avoid this and find setup.exe among the extracted content.
 Install it to the regular path. It will ask to start the IP Msgr once it got installed. Start it.
 Now to run another instance, in the run dialogue, type ipmsg.exe 1518 (any port number which should not be in use). That’s it. This creates another instance.
 Now if we want the other person to be exist in the same port, they need to do the same procedure. Then both users will be listed.
This is how you can run n number of instances. Another log will be created automatically if settings done in proper.
This is awesome. We never though it would accept port number on command line. Thanks Sriram.
Related : Voice Chat on Lan with Tiny Talk