What is a carrier lock?
From EjWiki
This is unlike a mobile phone (retrospectively called SIM-free or unlocked) that doesn't impose any SIM constraints.SIM locking is very common if subsidized handsets are offered with pay as you go contracts. It is crucial to note, however, that this technology linked with the mobile phone will have to be compatible with the systems being employed by the network carrier. A GSM cellular phone is only going to work with a GSM carrier and isn't going to operate on a CDMA service. Likewise, a CDMA smartphone can only work with a CDMA service and is not going to function on a GSM network. Keep in mind that modern (2013 and newer) top end cell phones are equipped to support both CDMA and GSM technologies, letting consumers to use their smart phones on nearly any network.
Unlocking Technology: Typically, a locked mobile phone will show a message if a restricted SIM is used, requesting the unlock code. On new phone models running Android operating system software, the smartphone is going to show a message saying “SIM network unlock PIN” or “Enter Network Lock Control Key” if it's network locked. Windows phones should display the message, “This SIM card can only be used on specific networks. Contact your customer service center for the unlock code”. Alternative handsets may well display assorted messages that include "Enter special code" or "Enter unlocking code," or in some circumstances the handset may simply show a message saying that it is locked. The minute a valid code is typed in, the mobile will display "Network unlocked” or “Network unlock successful”.
Economics: Mobile companies have commercial incentives both to bolster SIM lock security (which placates service companies and allows exclusivity offers) as well as to weaken it (broadening a device's allure to customers who aren't interested in the service provider that offers it). Furthermore, making it too hard to unlock a mobile might make it considerably less attractive to network service providers who've a legal duty to provide unlock codes for certain devices or in specific countries.
Unlocking Services: Lots of businesses offer a permanent smartphone unlocking service. This service needs individuals that would like to unlock a mobile phone to supply their IMEI number to a service supplier and frequently they will also request the country and service provider the phone is locked to, frequently sent through email or entered on their web-site. The organization will then supply (at a cost to you) the unlock code for the mobile.
Unlocking Service Providers: Regrettably there are a great deal of scammers online retailers working in the mobile phone unlocking industry. As a result it is prudent to make sure you locate a reputable supplier for this service. Do your due diligence and investigate all prospective dealers prior to choosing to place an order. In the case of on-line providers, make certain they document their registered company name and corresponding registration information (all authentic enterprise should be legally registered with all the official authorities for their country of origin) and ensure they give a legitimate listed address and contact details on their web-site. Additionally make certain that any payments made are done so thru legitimate methods as in a recognized bank or financial institution using a debt or credit card, but never make payment via a direct transfer since this provides no fiancial security.
