You need to make sure you're running the same server version as your friends are playing. If you're running the server manager for 1.0 and they have the 1.1 game installed.. they won't see your server. make sure your server is running on the internet and not set for a LAN. I'd also make sure your firewall isn't blocking your server or their connections.
It shouldn't matter that you have wireless internet... but it will matter if you've got a seperate firewall for the router. You usually have to go into the router configurations and clear the ports for server and game use or just DMZ the line your server is on. DMZ= Demilitarized Zone.. or clearing all the ports on an internet line. It's usually a configuration setting for routers for specifically clearing lines for server use. It'll be in your router docs. Each router is different so I can't be any more detailed than that.