Only for Europe versions of the offical Konami site:

Metal Gear Online Premiere Beta will be available as a free download on the PLAYSTATION® Store from April 17th (12:00 CEST) until May 6th (10:00 CEST).

US version has nothing, and is only available through pre-order Beta Keys.

Related posts:

1. IGN: Some MGO Beta Keys Invalid?
2. Euro PS Store for April 15, MGO beta on April 17
3. Funcom gets the hump about cancelled pre-orders - beta now closed
4. MGO Beta Available for Download
5. MGO Beta Free Download For All Europeans: No Pre-Order Needed