Asked by: Amy Rouse, via email

While smartphones are pretty smart, their ability to make and receive calls is due primarily to the clever network they’re in touch with. Known as the cellular network, it’s made up of thousands of masts across the nation, each able to pick up transmissions from phones in its vicinity.

By detecting whose phones are currently nearby (using each phone’s unique, 15-digit ‘IMSI’ code), they can send calls from other parts of the network. As we move, we enter the coverage area (‘cell’) of a different mast, which notes our presence in turn.

The cellular network also means that phones don’t have to be powerful: they only have to communicate with the mast in their local cell. The network does the hard work of transmitting the calls across the country and beyond.

How long before mobile phone SIM card combinations run out? © Getty Images

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Robert is a science writer and visiting professor of science at Aston University.