The head of telecoms firm O2 has apologised to customers for times when its mobile network has been overloaded by smartphone users.

Speaking to the Financial Times, chief executive of O2, Ronan Dunne, said he was “disappointed” with the company’s network performance in London since the summer. He blamed the problem on an increase in the use of smartphones and data-hungry applications, which has left some customers unable to connect to the internet, check emails or even make or receive calls.

Mobile phones such as Apple’s iPhone are becoming increasingly popular, with users spending more time downloading data from the web, which puts mobile networks like O2 under pressure. Watching an average YouTube video is said to have the same effect on a mobile network as sending 500,000 text messages and it’s estimated that data traffic across the UK is doubling every four months.

Dunne said: “Where we haven’t met our own high standards then there is no question, we apologise to customers for that fact. But it would be wrong to say O2 has failed its customers en masse.”

He said O2′s problems were largely confined to London, but smartphone users in the UK’s capital are not the only ones to suffer problems.

In New York, telecoms firm AT&T suspended online sales of Apple’s iPhone over the weekend, leading to speculation over the company’s ability to handle data traffic. AT&T has already admitted its network needs improving in certain areas such as Manhattan and San Francisco which it says is being handled as a matter of urgency.

The iPhone was available once again from AT&T’s website on Monday. The company declined to offer an explanation, except to say the firm “periodically modifies its promotion and distribution channels”.