[miki123211]

The Polish spin on this were unsecured office landlines that used radio for some reason, I don't remember if that was for cordless handsets or just an access technology.

People would walk around big cities, usually on Friday evenings, radio scanner out, trying to find one of these. They would then dial a premium-rate number, preferably on more than one line. In most cases nobody would realize that something was up until Monday morning, and if they had a way to disconnect the calls before then, not until the bill came.

You could do similar shenanigans with unsecured PBXs or insecure answering machines that had a "call my mobile if somebody leaves a message" feature.