Mobile phones in London
The UK uses the GSM phone system. This is the most popular system used in the world. Often when visitors come from the USA or Canada their phones will not often work. There are four major phone networks in the UK. Vodafone, O2 (formally known as Cellnet), T-Mobile (Formally One2One) and Orange. A New entrant into the market 3 (or Threee Mobile) has also begun to make some in roads into the market originally by offering video phones, but now favouring to offer customers phone with added features such as Skype, MSN Messenger, Yahoo Messenger & now Facebook access direct from your mobile phone.
Unlocking a mobile phone
In the UK it is usually pretty normal for a phone company to lock their phone to thir own network. This is to prevent you from putting the SIM of another company into that phone and making use of it. Most major brands of phones an be unlocked. Unlocking a phone is perfectly legal and in many cases the phone companies use it as a way to get more money out of the customer by asking for a fee in order to provide the customer with the unlocking code.