Unlocking a mobile phone is simply removing it's SIM card restrictions, allowing the phone to use virtually any SIM card from any network in London or anywhere in the world. This in turn has these benefits:

• Increased value. Most unlocked mobiles will sell for more as the person who's buying it isn't restricted to the network your phone was on.
• Freedom Abroad. Instead of paying expensive roaming charges from you home network provider, why not buy a local pay as you go SIM card and pay much less per minute! (Check rate before hand!)
• Change Network. If you like your mobile and don't want to change it just yet or just have an old phone in the drawer you'd like to use again. Unlock it to swap networks! 30 Day Sim Only contracts in London especially are excellent value at present.. Giffgaff Bill Pay Lite plans for instance.. or Lycamobile UK Pay As You Go Plans!!