If you tested it at home then it should work given the new IP address you list for the client of the server is a valid one. I assume for the home test you used, 127.0.0.1? Provided firewalls and the like, and port is available, it might be as simple as changing the localhost address to the new one.
I realized the above paragraph might be a slight repetition of my previous post Tim. This morning I just finished building a client/server app of my own which represents a chat room, likely similar to your IM'ng app. I'm pretty sure the IP address change I mention solves it - I know this because I tested mine via my local machine via 127... and I also uploaded it to my remote server and it was a success.
Let us know what you come up with
