BT is to roll out a phone box fit for the 21st century offering free calls and ultrafast Wi-Fi.

The ultramodern Link kiosks will open on major high streets across London next year complete with charging points, access to maps and tourist information.

BT said the rollout marked "the next evolution" of its public payphones and would bring digital innovation to the streets of London.

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Hundreds of BT's existing phone boxes will be replaced by the new Links, which will take up less space on the pavement, the telecoms giant said.

However they will be installed in smaller numbers than the payphones they replace, with "at least 750" appearing across central London and other cities over the next few years.

Users within range of a Link will be able to access free ultrafast Wi-Fi with speeds of up to 1Gbps, and the kiosks will offer free UK landline and mobile phone calls, mobile device charging via two USB charging ports and a touch-screen tablet for accessing maps, directions and local services.

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The Links will also have sensors to capture real-time data relating to the local environment, such as air and noise pollution, outdoor temperature and traffic conditions, with potential for the information to be fed into smart services.

BT said the service would be funded by revenue from advertising on the Links' digital displays.

Rajesh Agrawal, London's deputy mayor for business, said: "I welcome this exciting new addition to London's streets.

"Expanding London's digital infrastructure is a priority for the Mayor, and LinkUK can play a big part in improving connectivity for Londoners and visitors to our city, while reducing street clutter by upgrading and reducing the number of phone boxes.

"London is already widely regarded as one of the technological capitals of the world but the Mayor is determined to improve connectivity across the city to ensure we maintain that position."

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BT chief executive for wholesale and ventures Gerry McQuade said: "We're evolving the phone box to make it relevant in the 21st century by offering people ultrafast Wi-Fi and a range of digital and information services entirely for free.

"London is one of the greatest cities in the world and it's entirely fitting that it becomes the first UK city to benefit from the Links. But we will be rolling out many more Links to the other great cities across the UK over the coming months as we look to transform the look and functionality of our public payphones."