Fredrik Thylander the Senior Designer at DICE has recently revealed that in Battlefield 3 there will be co-op unlocks, which players can use in multiplayer.
When Thylander was asked on the social networking website Twitter about the unlocks for co-op and multiplayer he revealed, “There’s about 6 or so guns for various classes (or all) to be gotten for MP from playing coop. Like the M39 EBR”.
Thylander went on to mention that these unlock can’t be unlocked via regular multiplayer mode “but they’ve been carefully selected to make sure there are other, similar, pieces of equipment available through pure MP.”