So with the shutdown of the GameSpy servers recently, many games have lost their ability to play in multi-player mode.
Unfortunately, UT3 is one of those games. There is good news though. A patch has been released in the forum that points the client game and the home made servers to a replacement Master server thus keeping UT3’s multi-player functionality alive!
The patch can be found here: epicgames.com-Gamespy-Patch
Game Reference: Unreal Tournament 3