Once upon a time, the post office decided that they didnt want to run these big expensive heavy cables out into the wopwops.

Running a telephone line over 5kms gets tedious and voice quality suffers.

So the PCM pair gain system was invented - in NZ these are usually Alcatel systems.

A digital PCM system of a few pairs which carried 2mbits for 2kms, would then be repeated every 2kms until it gets to one of these white cabinets.

At the white cabinet, the digital 2mbit signal is converted back into analog lines, which could then go 5kms from that cabinet.