ISDN bills could be problematical.......
I used to work for a large car auction company, with a head office up-north, and the flagship office (where the CEO lived) down in the south-west.
As lead-techie, I had provisioned a state-of-the-art Video Conferencing system that used 3 ISDN lines (6 channels) bonded for comms (ground-breaking - if not pocket-stretching at the time. IP-based VC wasn't offered at the time.
Worked amazingly and paid for itself in short-shrift.
However......
One day if developed a silent fault which seemingly went on for quite a while.
We only knew when a lorry (I kid you not) delivered our phone bill on pallets.
It was a not-inconsequential amount.
Red faces all around, but pretty sure it cost nearly as much to print and transport the bill, than it did to cover the cost of the ISDN.......