I often play SWC at university, which has an open network connection, so thousands could be online at the same time. I don't know if there are other SWC players on this connection, but I wondered if a wireless network like this one is something that I need to worry about registering as a multi or not?
You will not be banned if by some highly unlikely fluke another player shares a University connection with you without your knowledge, or at least not for long, once the multi admin has looked into it they will inform you both so that you can register as multi's if thats the case.
“I heard that you have to register as a multi account when sharing the same IP adress
except when you're at a college. How they know it's a college I have no idea.”
As Ten says, if you know you share a connection with another player (even if it's at a college), you need to register.
The "except at a college" thing you are thinking of is probably the general proxy detection SWC uses, that allows them to determine if two players sharing an IP address are connecting via a public proxy, like a university or military connection, or a number of ISPs such as AOL. Those proxies cause you to display with the same IP address as another user, even if you have no idea someone else is sharing the connection - and it is in that instance that you would be unbanned (or possibly not banned in the first place, depending on the circumstances). It does not negate the need to register with another user if you are aware of them, however.