You do get attachments from battlepacks as well as from unlocking.
I have personally gotten the Cobra, prisma, grips, lasers and JGM from the battle packs.
You get the packs by being a premium member, having pre-odered, leveling a level 3, 5, 7, 10, 12, 14 (and so on).
You get weapons packs by getting a certain number of kills with a specific weapon (210 first and then every 50 kills)
Some attachments are only available in the battlepacks
Battlelog list all this information in you unlock progression and actually pretty good. It's worth signing up for it.