There are a lot of regional differences, so bare with us while we flesh out the details.
In North America, those that pre-ordered SOCOM 4 will get first-access to the beta on August 4th. They will be followed by European PlayStation Plus subscribers on August 10th. Finally, North American PlayStation Plus subscribers will be able to jump in on August 23rd. For a full breakdown of the schedule in your region, refer to the North American or European PlayStation Blog.
The beta will consist of two maps, including Glamorgan, Wales (seriously!) and Bogota, Colombia. You'll get to check out two of the multiplayer modes, Team Deathmatch and Chain Reaction. The level cap for the multiplayer beta is level twenty, with all the weapon and character customisation from the full-game included in a limited format.
Don't worry if you're not a SOCOM fan or PlayStation Plus subscriber, there will be other ways to get into the beta. Typically Sony hands out a variety of codes to various publication, so just make sure you're keeping your ear to the ground if you want to get in that way.
The game's out in September.