It has been revealed that when you pre-order a copy of Battlefield 3 from Elctronic Arts web store Origin, you will receive access to the BF3 beta when it is made available in September.
“Open Beta for Battlefield 3 (Origin Exclusive)
Players who pre-order the game from Origin will be granted early access to the Open Beta for Battlefield 3 when it goes live in September 2011.”
Click this link to check out the Battlefield 3 Origin page.