In an interview with Gamerzines Battlefield 3 senior producer Patrick Bach said that the game will likely use some kind of online pass. That is a key which can only be used once to unlock multiplayer features.
If you want to loan out the game to a friend or sell it on, the other person will have to purchase a new online pass in order to play online with others. EA have used this solution in the past, mainly in order to impede used game sales or at least for the publisher to get something out of a used game sale.