Cell phone companies generate and attract new customers byoffering free phones to new customers who sign lengthy contracts.These phones are designed to require a Subscriber IdentificationModule known as a SIM card. This SIM card is simply a microchipdesigned to store data from the subscriber. SIM cards can be placedinto any phone to provide cellular service. Locked phones onlyrecognize SIM cards from a certain carrier, but unlocked phoneswill recognize a card from all carriers. Discounted and free phonesoffered by carriers are usually locked to make them loyal to thecarrier and make the phone unable to be used by anotherprovider.Getting a PhoneAlthough these unlocked phones are very close to full-retailprice, many find being able to use them with any carrier that usesSIM cards an advantage