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From June, almost all Londoners should be able to get free Wi-Fi access in London Underground stations, after O2 became the latest major carrier to sign up as a wholesale customer of Virgin Media.

Virgin Media has been providing internet access in Tube stations since the Olympics in mid-2012. The service was initially free for all, but after the Games, Virgin started charging on a daily, weekly or monthly basis for those who aren’t customers of Virgin Mobile or the company’s fixed-line services. EE and Vodafone – respectively, the UK’s first and third-largest mobile carriers — signed up as wholesale partners in November, ensuring that their customers would also get free access.

O2, the second-largest mobile operator, has now done the same, with its customers getting access from June. According to Virgin, those three carriers account for 89 percent of London’s population, leaving only overseas tourists and subscribers of other carriers – notably the smallest of the big four, Three – having to pay up for access.

“Having O2 on board is excellent news for the thousands of people that use the Tube every day,” London Underground strategy chief Gareth Powell said in a statement. “Most customers will now be able to access live travel information or use social media to plan their social life while on the move.”

London Underground also used the announcement to reveal 12 more stations that will be Wi-Fi-enabled, including Baker Street, Bank, Earl’s Court and Sloane Square. The total number of stations bearing connectivity is now 120 (the Tube network has 270 stations, although many aren’t in central London, as the Wi-Fi-enabled ones tend to be).

I’ve asked Three whether it’s talking to Virgin about getting its customers into the scheme, and will add the response in when I get it.