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The advent of carding meant you could telephone your friends in the US or UK and have a long voice conference call with all of them simultaneously—something which could be a lot tougher to arrange on a PABX.

Using a PABX, the employee of a large company could dial another employee in-house without incurring the cost of a local telephone call.

Sometimes phreakers made free calls out of PABXes simply by exploited security flaws in a particular model or brand of PABX.

In fact it was a lot less hassle than manipulating some company's PABX.

A PABX, a private automatic branch exchange, works like a mini-Telecom telephone exchange.