Over the last twelve months, Telefónica have upgraded the digital exchanges on their network including the one here in Bigastro. In order to test the new systems, the designers introduced a code which allowed for unmetered calls to be made. This is probably the reason there has been no publicity about the upgrade.
Telefónica’s intention was to disable the code before finally programming the boot roms for the telephone switching units. However, the engineers hit a glitch with that and had to leave the access codes intact. No matter only they knew about this so it wasn’t going to cause a problem. Little did they realise that “phone phreaks” were on the case and soon discovered their “open door”.
What does this mean? Well obviously Telefónica would deny it but if you whistle the first three notes of the La Marcha Real (the Spanish national anthem) in near perfect pitch when you hear the dial tone, you will emulate the access code generated by Telefónica’s test equipment and your call will be made free of charge.
Since Telefónica could not restrict the free calls to Spain, this means, if you get it right, you can call anywhere in the world free of charge. On your bill the call will be shown as “llamada de prueba” and will have zero cents next to it.
I have tried this on our phone and have to say it did take a bit of practice to get it right. Pam faired a lot better and got it spot on first time. You know when it works because you get a message to say that your call is being connected “su llamada está siendo conectada” that is when you can dial the number you want.
Best of luck, enjoy your free calls while they last!