<i>SIM lock: </i><br /><br />A SIM-LOCK, network lock, CARRIER-LOCK, IMEI-Lock or (Master) subsidy lock is actually a technical constraint built into CDMA and GSM mobile phone devices by producers to be used by carrier networks to restrict using these phones to a particular countries and/or networks. This is unlike a cell phone (retrospectively called SIM-free or unlocked) which doesn't impose any SIM limitations.The reason why a lot of network providers SIM lock their devices is that they offer phones at a discount to customers in return for for a contract to cover the use of the network for a specified time period, typically between one to three years. This business model permits the company to recoup the price of the device over the life of the contract. These discounts are worth close to hundreds US dollars.<br /><br /><br /><i>Unlocking Technology: </i><br /><br />Typically, a locked phone will show a message if a restricted SIM is used, asking for the unlock code. On recent phone models operating on Android software, the cell phone will show a message stating “SIM network unlock PIN” or “Enter Network Lock Control Key” if it's network locked. Windows phones are going to show the message, “This SIM card can only be used on specific networks. Contact your customer service center for the unlock code”. Alternative devices could display alternative messages which include "Enter special code" or "Enter unlocking code," or in some circumstances the mobile will probably show a message saying it's locked. As soon as a valid code is typed in, the mobile will display "Network unlocked” or “Network unlock successful”.<br /><br /><br /><i>Economics: </i><br /><br />Most of the time a SIM-locked device is sold at a noticeably lower cost than an unlocked one simply because the service provider plans income thru its service. SIM locks are used on lower priced (pay-as-you-go) handsets, though discounts on more expensive handsets demand a subscription that provides guaranteed income. Unlocked mobile phones have a higher market value. <br /><br /><br /><i>Unlocking Services: </i><br /><br />Plenty of businesses provide a on-line unlocking service . This service needs individuals that need to unlock a mobile phone to give their IMEI number to a service supplier and often they will also need the country and cellular network the mobile phone handset is locked to, either sent through email or submitted on their web-site. The company will then supply (at a cost to you) an unlock code for the device. <br /><br /><br /><i>Unlocking Service Providers: </i><br /><br />Regrettably there are a multitude of fraudulent sellers active in the smart-phone unlocking industry. Consequently it is prudent to make sure you find a reliable service provider for this service. To assist with the search for a legitimate service provider, we've supplied an inventory just below (and in no particular order) of a number of legit organizations currently offering such services.<br /><br /><br /><i>Reputable Mobile Phone IMEI Unlocking Service Providers: </i><br /><br /><br /><ul><br /> <br /> <br /> <br /> <li> Unlock Base </li><br /> <br /> <br /> <br /> <li> Unlock River </li><br /> <br /> <br /> <br /> <li> Cell Unlocker </li><br /> <br /> <br /> <br /> <li> Mobile Unlocked </li><br /> <br /> <br /> <br /> <li> DoctorSIM </li><br /> <br /> <br /> <br /> <li> Unlock.Zone </li><br /> <br /> <br /> <br /></ul><br />