Yes, leave your name and number with them - you can walk around the museum or even leave until you get a text saying its your turn. Don't venture too far out though, they only hold the spot for 20 minutes!
There's a machine to get a ticket
Make sure to get there early in the day to guarantee you get a spot in the mirror room. We got there by 11: 00am when the Broad opens, and only had to wait 30min before we got into the mirror room.
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