Relocating vast numbers of subscriber lines is something to be avoided.

In 1929 Indiana Bell realized they needed a larger telephone exchange (“CO” to use the US term) to meet growing demand, and while there was vacant land around the current building, it wasn’t large enough to build on with the current building slap-dab in the middle of it.

So rather than relocate the subscriber lines to a newly built exchange, they just moved the exchange to the rear of the block, to free up space to build a larger one.

Over a 4 week period engineers shifted the working, 8 story steel and brick telephone exchange, still fully staffed, around to the other side of the block, without any interruptions to the subscribers served from the exchange.