The beta will be only accessible to Xbox Live Gold subscribers. At this time there are no plans for the beta to be released for the PS3 and PC.
An EA representative confirmed the news:
The limited beta program is focused on one platform for Danger Close Games to test various multiplayer components in preparation for the launch on October 23 including online gameplay functionality, enhancements to the free Battlelog social network, and stress testing.
The beta will include the HotSpot multiplayer mode where players attack or defend (depends on what team you are on) random locations on the Sarajevo Stadium map in Bosnia.
Downloading and playing the beta also has some perks attacked. Once the total downloads of the beta hit the three million mark, the new music video by Linkin Park for Castle of Glass will be unlocked ahead of release.
In addition each player will be given access to Double XP for 60 minutes of gameplay when the game launches.