WoW.IncGamers is speculating that the World of WarCraft: Wrath of the Lich King beta may begin in June:
These World Wide Invitationals by Blizzard have increased in size since they started some 4 years ago. Honestly, who even knew there was one in 2006 before they shocked everyone last year with StarCraft II in Korea? One change from last year is that they haven’t actually said they will announce anything new and big. That could mean that they just haven’t said anything yet, and some game is on the way (as June is still far away), or things are just as simple as it looks: There are no new games to be announced this time around.

That tasty bullet point; “And more…” is very alluring though! A lot of hints point at Blizzard starting a Wrath of the Lich King Beta (and/or StarCraft II Beta) shortly after WWI, or that they will announce a Beta Date during the event. Meanwhile, we can see that the StarCraft II production is coming along nice as well, and all those Q & A sessions (157 thus far!) with Karune & Xordiah certainly suggests they want to be as proactive as possible with the StarCraft II community.

From:

http://ve3d.ign.com/articles/news/36834/Wrath-of-the-Lich-King-Beta-in-June