Above video shows the Half-Life inspired dramatization of how to disassemble the classic German yellow phone booth (replicas only of course, and only for educational purposes).
It’s a piece of cake to take off the top, the door, even the floor. There’s a very limited number of bolts that need to be removed by counter-boring to get the floor and top removed, everything else is held together by screws. But once you’re left with the three remaining sides, things get tricky.
Here’s how you do it.

All round corners are clipped in place but the clip needs some force to get unclipped (the metal thing pried loose in the video is one half of the clip).
We’ll start off with the easiest of the four corner pieces, the door hinge. You do not actually have to remove this part, but it’s first of all quite easy to do and it gives you nice insight into what the clip mechanism looks like, which is crucial to understand to allow you to remove the rear corner pieces.

1. Remove the three screws holding the round corner piece of the door hinge in place.

2. The door hinge corner piece can be pried loose easily once the screws are removed (use crowbar).
   Now, for the two rear pieces.

3. Use a crowbar to push the corner upwards by around 2 to 3cm.
   You can do this by placing the crowbar between the rounded-off top of the rear corner and the two side walls and use it as a lever to push the corner upwards.

4. Force the crowbar down into the gap you just created and try to unclip the top most clip.
5. Start pulling on the corner piece in a diagonally outward direction.
6. While pulling, use the crowbar to pry each clip loose from top to bottom.
7. Once the corner piece is gone, remove the screws holding each clip in place.
8. The clips now pull right off the corner, allowing you to take the walls apart.
   Disclaimer: two phone booth replicas have been slightly hurt in the making of this video.