We mentioned some time back that EE and Vodafone has joined Virgin Media in offering free Wi-Fi for London Underground. But now O2 is joining in too.Yes, as of this week, O2 customers get free Wi-Fi on the London Underground too, as opposed to being faced with a bill for the privilege. That's good news if you got used to using the service when it was free, which was from the London Olympics to the start of this year.With Vodafone and EE doing a deal with Virgin Media for free use of the service, it left O2 out on a limb and lacking a key selling point in the capital. With that in mind, it sounds like the network has been forced to pay out to Virgin Media on behalf of its customers. Nice touch.That just leaves Three. Peer pressure might force that through too, although there's no hint of a deal yet.On top of the O2 news, Virgin Media has also announced a new batch of stations which will have free Wi-Fi from this week. Those being Acton Town, Baker Street, Bank, Caledonian Road, Earl's Court, Holland Park, Ladbroke Grove, Maida Vale, Queen's Park, Shepherd's Bush, Sloane Square and West Ruislip. If any of those are near you - log in now for free! Unless you happen to be using the Three network, obviously.