Dealer should call when the paperwork comes in. If you have a lazy dealer then you may call ATF to do your own legwork.
Thanks for the answer. If I may ask further, when you say the dealer should call when the "paperwork" comes in, you mean the actual stamp itself, or is there some other paperwork they get before that? I ask because I see so many people who know they've been approved, but are still waiting for the stamp to arrive. I'm wondering how they got notice of approval if the stamp hasn't made it to the dealer? Unless they are calling every week to ask their status, in which case, it would seem that only bogs down the system further and makes the whole process even longer if everyone did that.