Do you know what these are? These are slots for pay phones. Empty slots, as you can see. They are in the Texas Capitol Extension (underground). When the extension was built (completed in 1993), each slot housed a pay phone. There are at least two of these ghost pay phone clusters in the extension, one on the Senate side, one on the House side.
These slots still get some use, even though the pay phones have been gone for years. Some people use them to set their papers, briefcases, food in while they are talking on their cell phones.
My, how times have changed.