Season 4 starting on Jun 24

It is also worth noting that this season will herald new Arena ratings requirements on most Season 4 gear, including many of the new honor rewards. In addition, Season 3's shoulder and weapon Arena rating requirements will drop slightly, all season 3 gear will cost fewer arena points, and the Season 2 gear will be purchasable for Honor. Season 1 gear will be gone forever, so buy it now if you want it for looks. This is also very likely to be the last season before WotLK comes out. There is still no word on what will happen to the gear after that - whether it will be discarded completely for new level 80 gear, or left as an option for people who prefer to stay at level 70 or do not buy WotLK.

http://www.wowinsider.com/2008/06/10/arena-season-4-set-to-begin-on-june-24th/

Original blue announcement:

http://forums.worldofwarcraft.com/thread.html?topicId=7102930387&sid=1