I already wrote what it was like to use the internet when flatrates were not invented and how i stayed online 24/7 anyways without paying a few grand on phone bills ( Why hackers loved AOL ).
Well even before the internet went public many people were online and many of them didn’t feel like paying a fortune for that.
In Germany paradise was actually closed on January 1st 1980. Before that a local call was always just “one unit” which was something like 5 cent. the thing was that the unit did not have a time limit. So you could connect to any other local modem virtually forever, costing you like 5 cent. Back in the late 1970s the popular BBS (Bulletin board system) came up, so just when it became fun to be on-line (back in the days you would write it with a dash) it was over again.
Actually in Western Berlin (Which held a special role until the German re-union) local calls were still “unlimited” until 1992. However the rest of Germany (And other parts of the world) needed a solution. And the solution actually came much earlier – from desperate U.S. users – namely “John T. Draper” aka “Captain Crunch”.
John Draper aka “Captain Crunch” discovered that a whistle included in the famous “Captain Crunch” cereals produced nearly exactly a 2600 Hz tone – which was coincidentially also the exact frequency of the “operators” dialing console to trigger a long distance call. In a nutshell – you could call a local or free phone number, send the 2600 Hz tone through the phone line and then dial the long distance call number being only billed the cheap (or free) call. The mechanics behind this were already published in 1971 – but for obvious reasons they didn’t become that common in Germany before January 1st 1980. But yeah by then even the Germans saw how useful this technique is and it stayed very common until the early to mid 1990s when phone companies finally moved to “out-of-band” signals for routing phone calls.
Until then the 2600 Hz tone was so popular among “computer freaks” – some people even managed to whistle in 2600 Hz, some had tropical birds trained to whistle 2600 Hz, the 2600 Hz tone was on loads of audio tapes, there were selfmade (and “kit”) electronic devices around to produce it, there were toy whistles and with the popularity of sound cards and home computers with sound abilities there were obviously also numerous appz to produce the wanted frequencies. In the early 1990s most people in the “warez” scene used blueboxing to download tons of games and appz without having a high phone bill.