We naive Americans apparently think that’s what they’re for, according to London’s deputy mayor. BBC NEWS | UK | England | London | Sex card challenge to phone firms Kit Malthouse, London’s deputy mayor for policing, wants the numbers on sex calling cards found in telephone boxes blocked as soon as they are identified. He said mobile phone numbers were valuable to those behind the sex industry and should be cut off. The deputy mayor has invited Vodafone, Orange, O2, 3, Virgin and T-Mobile to meet him. Mr Malthouse said: “If you are an American tourist and if you walk…