LONDON, England — THE head of mobile phone operator O2 has apologised to customers in the British capital who were unable to make calls after the group’s network was swamped by people using smart phones such as Apple Inc’s iPhone.

In an interview published in the Financial Times newspaper yesterday, O2 Chief Executive Robert Dunne said some customers in London had periodically not been able to make or receive calls or transmit data because of pressure on the network from such smart phones.

The network problems in the second half of the year were blamed on increased use of applications by customers with smart phones that repeatedly pull data off the Internet at short intervals.

However, O2 said the situation had improved during December after it invested £30 million (US$48 million) in improving the network capability.

In the United States, the iPhone’s exclusive carrier, AT&T Inc, also has had trouble keeping up with wireless data usage, leading to dropped connections and long waits for users trying to run programs on their devices. AT&T has acknowledged that its network is overburdened with iPhone users in New York and San Francisco.

The company’s decision to suspend online iPhone sales to New Yorkers over the weekend led to speculation among bloggers that AT&T was trying to manage data traffic, even though the ban was more likely an attempt to curb buyers who renege on the service contracts and resell the phones in other countries. AT&T would only say that it periodically “modifies” its distribution channels.

O2’s exclusive contract to market the Apple handset in Britain expired in November.

“Where we haven’t met our own high standards, then there’s no question, we apologise to customers for that fact,” Dunne was quoted as saying in the Financial Times. “But it would be wrong to say O2 has failed its customers en masse.”

Nick Wilkins, a spokesman for O2 in London, said the company had seen “a huge explosion in data usage on the network in terms of Internet capability” and it had made moves to address those changes.

Wilkins said that the company had seen an 18 per cent increase in data traffic since the start of the year and that it continued to double every four months. “We are always investing in our network,” he said.

O2 said it has addressed the problem by working with its infrastructure supplier Nokia Siemens Networks on software modifications, installing 200 additional mobile base stations in London and holding discussions with the smart phone manufacturers to learn more about applications that could place heavy demands on its network.

O2, which is owned by Spain’s Telefonica, is Britain’s largest mobile phone operator, with 21 million customers.

Vodafone, Britain’s second- largest mobile phone operator, has claimed its network can cope far better with the rapidly increasing number of smart phones.