Found this Battlefield: Bad Company 2 getting 4-player co-op -- PlayStation Universe
Four-player co-op is heading to Battlefield: Bad Company 2 with Onslaught mode. This mode will allows teams of up to four players to join together in co-op mode, meaning you can practice your skills without players attacking you at the same time.
The Onslaught mode brings four multiplayer maps, Nelson Bay, Valparaiso, Atacama Desert, and Isla Inocentes, and redesigns them with features like new lighting, vehicles, and a dedicated gameplay focus requiring teamwork.
"We're thrilled to bring something new and fresh to Battlefield: Bad Company 2 while still keeping Battlefield's signature gameplay intact," says Patrick Bach, Senior Producer at DICE. "We want to consistently support the over 4 million fans playing the game with new ways to get into multiplayer and also challenge the elite players with new experiences to improve their performance online. Effective squad play is the key to success in Battlefield: Bad Company 2 multiplayer and this new mode will provide players with a dedicated environment to test their team skills and rank against the competition."
There is no specific release date, other than “coming soon,” but we do know the content is heading to both PlayStation 3 and Xbox 360