A Blue Box, made circa 1972 by future Apple founders Steve Jobs and Steve Wozniak, is due to cross the block at Bonhams.

It’s valued at up to $50,000 ahead of the December 6 History of Science and Technology sale.

The Blue Box was designed to hack into the phone network 

The device was designed to be used in “phone phreaking”, a way of hacking into telephone operators’ dialling systems.

During the 1950s, the original phreakers worked out they could get free long distance calls by mimicking the operators’ dial tones.

At first this was achieved by whistling.

The first Blue Boxes arrived in the 1960s and performed essentially the same task, enabling hacking to be carried out more easily.

While studying engineering at Berkeley, Wozniak and Jobs became fascinated by phreaking.

This digital Blue Box, the world’s first, was the first thing they designed in partnership. They spent hours relaying their way through the global telephone system.

Wozniak once managed to get through to the Vatican by pretending to be Henry Kissenger.

The pair started manufacturing the (highly illegal) device, selling it door to door to their fellow students. They made around $6,000 in profit.

Jobs would later say: "If it hadn't been for the Blue Boxes, there would have been no Apple. I'm 100% sure of that...

"Woz and I learned how to work together, and we gained the confidence that we could solve technical problems and actually put something into production."

Four years later, Wozniak came up with the revolutionary Apple-I.

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