Kimberly Suiters of WJLA Channel 7 (ABC-affiliate) in Washington DC discussed the practice of landline phone “slamming” which can be very disruptive to businesses, link here Business find their line suddenly moved to another (long distance) provider without authorization, and then , due to a catch-22, they can’t get an answer from the original provider. There is a link to an FCC page on the problem. I think I've heard the word "cramming" too for this.
The issue became more common in the 90s as people began to switch providers for “deals” before cell service became so popular.
It’s not “cramming for an exam”.