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.
At the time the global population was seven billion.
"In 40 years we’ve moved rapidly from the mobile phone as a businessman’s tool, through consumerisation and internet access to everything being connected," Dr Mike Short CBE, former president of the Institute of Engineering and Technology and Vice President of Telefonica Europe, told the BBC.
"In the future we will see a much wider range of devices – many of which will be wearable," he added.
"We will work more fully with all the senses. The move to glasses has begun – how can we use eye control to change and look at pages?
"Wearables, in terms of (smartphone) watches, are coming. We’ll also see health measurement body vests that can communicate with your phone and then your doctor," said Dr Short.