Demonstrates a clip originally mentioned by BoredOfYou. Found by accident after starting the game and have not been able to set it up again. However, once I got Jimmy in a clipping state I was able to easily do it a second time, as shown.
Also shows walking on a thin ceiling beam and jumping to angle Jimmy while not falling off like sidestepping would do.
The other phone box's cutscene, which moves you but lets keep your height if you immediately press Esc, clips your head into the ceiling, so you can now escape the room's bounds by jumping. There's nothing to find OoB without your jetpack, Rocket Ship, or other flying equipment, though. Seems like you can fall for quite a while, though I haven't waited to see if Jimmy lands, wraps around, or is just stuck on the lowest height value but still doing a falling animation.
Use this verification movie, this XML, and this CONF to play back. Unfortunately, due to apparently specific intro timing, I haven't been able to resync this to any other verification input or HDD after days of effort, despite it running laggy on 250k cycles and 48MB RAM. These tricks wouldn't be used here in an any% anyway, but could apply elsewhere if lightning strikes again for this clip.
Encode of the important part: