(Note: Move this post if this is the wrong forum.)
A friend pointed this out to me earlier today, but if you read the newest Important Information on the PlayOnline website, they mention that the next update will have "/tell" filtering implemented.
Source: FINAL FANTASY XI Official Web Site
http://www.playonline.com/ff11us/imgs/info/infhr.gif
We have confirmed that RMT and suspicious site advertisements are being sent in large quantities as tells in game.
Regarding these issues, we ask that when you place a GM call to report them, that you please include the name of the character that sent you the tell in the call summary. Additionally, while we are investigating all calls that come in, we estimate that the number of calls will continue to increase by a considerable amount, so we ask for your understanding if a GM is unable to personally respond to these issues specifically.
To counter the increase of these issues, we are planning to introduce a filter to block suspicious tells along with the next version update. We ask for your patience and understanding in this matter. A little late are we, SE? Difference between this and the "ChatMon" plug-in for Windower is that both PS2 and 360 users finally get "/tell" filtering.
I guess that's good news.