You can setup your own public Minecraft server. Follow the simple steps below
Before proceeding with this tutorial, make sure you have the following:
Download the Multiplayer beta server software at
http://www.minecraft.net/download
Notice, if you download the .jar version, you must launch it as “java -Xmx1024M -Xms1024M -jar minecraft_server.jar nogui”
Go to http://portforward.com/scroll down and find your router model number.
Skip the advertisement by clicking the “Click here to skip this advertisement…” link.
Scroll down and find the “Minecraft server” link
Follow the tutorial on how to port forward a Minecraft Server.
To get the IP of the server, go to www.whatsmyip.organd get your computers IP.
Add:25565 at the end of the IP. Ex: 1234.123.12.1:25565