The IBM Simon smartphone went on sale on the 16th August 1994, combining mobile technology with a wide range of computing features.
To mark the 20th anniversary, London's Science Museum is putting it on display in its new Information Age gallery, to act as a reminder of a different era which was free from constant connectivity.
Curator Charlotte Connelly said: "The Simon wasn't called a smartphone back then.
"But it had a lot of the features we see today. It had a calendar; it could take notes and send emails and messages and combined all of this with a cell phone."
Weighing in at 500g (1.1lbs) Ms Connelly said at the launch in 1994 that the design of the phone was well ahead of its time.
She said: "It looks like a grey block but it's not as big as you'd imagine.
"It had a stylus and a green LCD screen, which is similar in size to the iPhone 4. In fact, it's not a bad looking thing."
IBM's product was the first mobile phone to feature software apps and could be linked to a fax machine. The phone was only available in the United States, operating within a 15 state network.
Ms Connelly added: "It only had an hour's battery, it was $899 and there was no mobile internet at the time. So it wasn't very successful."
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