CALLING LONDON

Although the typical red phone box still exists in London, there are also many internet kiosks which enable you to surf the web, check and send emails in addition to making both international and local calls. Details are on the British Telecom web site.
HOW TO CALL LONDON FROM THE UNITED STATES
Some U.K. hotels have a toll-free number that you can call from the U.S.A. This is in addition to their usual toll-free number for calling from within the U.K. The number should appear on the hotel's website which can be accessed through the Rick's List.
London telephone numbers consist of eight digits starting with either the number 7 or 8. If you are ringing within London, just dial the eight digit number.
If you are calling from America, you first need to dial the code to get you out out of the states - 011. Then dial the code for the United Kingdom - 44. Then dial the London area code - 20 - followed by the 8 digit number beginning with 7 or 8. For instance if the London number is 7333-3333, you would need to dial 011-44-20-7323-3333 from the states.
If you are calling a London number from within the U.K. but from a different city in the U.K. you need to dial 020 before the London number - for instance 020-7333-3333.
HOW TO CALL A MOBILE PHONE IN THE U.K. FROM THE U.S.A.
Mobile phones in the U.K. begin with a zero. In order to ring them from the USA you need to add the country code and drop the zero. For instance, if the mobile number is 07742123456, you would need to dial 011-44-7742123456. If you are sending text messages, check first with your mobile phone contract provider to make sure that your phone will accept/send text messages to/from the U.K./U.S.A.