I took ze boyfriend here for his birthday and it sure was a treat for our first time!
I texted the special number a good week in advance and was told reservations are max of 6 people. They only hold your reservation for 15 minutes so be on time! When you get to Commonwealth, skip the line and let the doorman know that you have a reservation and just provide the name. After you get in, text the mystery number again and they'll instruct you on where to meet them.
Once you're inside, it starts to make sense on why reservations are a max of 6. Very intimate setting but entertaining as well, as there might be a piano man and usually a fun bartender to carry on a conversation with. There's 2-3 tables with a few seats at the bar. They of course have specialty cocktails that are era specific. My favorite is the Moscow Mule. We made friends with both the piano man and bartender so you can imagine our first time was definitely very enjoyable.
This is definitely a place where you can get away from the crazy drunkards screaming and hollering down Fremont, and just enjoy a nice cocktail.