What Is It?

[Nolan Kienitz]

OK, I got the telephone nook, phone book slot, etc., etc..

Now what about the trap-door and sliding board or board that 'folds down and out'?  Maybe a "gossip bench" ??

 

[Bill Kibbel]

It is a fold-out seat for use whilst on the phone.  I've only seen them directly below the phone niche.

[Les]

said some really nasty things, whilst sitting on that device!