AION closed beta event no. 3 is about to start. In celebration of Fourth of July and Canada Day it is scheduled to last longer than the previous two events – from July 2 through July 6. It is supposed to start in less than 15 minutes (12:00 PM PT, 9:00 PM CEST, 8:00 PM BST) and to participate you need to be one of the lucky winners of contests that have been running all over the net in the past few weeks (Fileplanet, Mmorpg.com and a lot more sites had some of these running).
The alternative is to have preordered the game through one of the officially supported retailers (some have digital downloads available). For US version check this page out while EU players should go here to preorder. You might want to wait a bit for our first impressions tho :).