Mobile phone celebrates 40th anniversary
3 April 2013 Last updated at 14:23 BST
The first mobile phone call was made 40 years ago today, on 3 April 1973.
Martin Cooper, a senior engineer at Motorola, called a rival colleague at another telecoms company and announced he was speaking from "a 'real' cellular telephone".
In 2012 a report carried out by the International Telecommunication Union found that there were six billion mobile phone subscriptions worldwide.
Simon Gompertz reports.