Mobile phones are usually locked to a particular phone network (unless they are SIM free in which case they can accept a SIM card for any mobile phone network).
Most phones available can be unlocked, that is, made to allow any SIM card, by simply entering a unique number into the phone. Many sites offer an unlocking service based on the IMEI (serial number) of the phone.
Unlocking can be as cheap as £5 and usually just requires an unlocking code which can be bought online.
NB. UKMobilesOnline.info cannot be held responsible for damages to mobile phones caused by any unlocking attempts.
