The price of the calls was the major obstacle to many hackers. In fact, it was probably the nightly switch to cheap calls at 6pm that saved an lot of British companies from major attacks during office hours. But there's a way of penetrating systems, or at least gaining the requisite knowledge to enable you to do so, which is very cheap indeed. I refer to the art that hackers call 'social engineering'. You may think that anything social is beyond the realms of your typical spotty teenage hacker, who spends all day watching sci-fi movies and all night grocking Unix.
Social engineering is different.
Conning confidential information out of people on the phone by pretending to be someone else doesn't count as proper socialising, so even hackers can do it. In the past, social engineering was tough. Finding out sufficient basic information to warrant making that first call was rarely easy, and often involved rummaging through dustbins or hanging around outside offices late at night. But not any more. The Internet has changed all that, thanks to the daft rule that forces companies to divulge so much useful information when they register a domain name.