All good things have to come to an end at some point and it comes with great sadness that on the 16th June, 2009 the UTAN server will be switched off permanently.
UTAN supports Unreal Tournament 2004. A game which is now, as given by the title, rather dated. The number of users of UTAN has, as expected, dwindled over time and it is no longer viable.
So that's that. If you have the addon installed, it will no longer work beyond the 16th, so it is recommended that you uninstall it as soon as possible so that you server's performance is not effected.
(source : xraygaming.com
, the site where UTAN is hosted)