Many of you are still in the woods about this whole unlock thing.
The lock we are talking about here is called a "subsidy lock". As we all know it's a method of keeping that phone to only operate with the carrier's network.
There are two network modes being used in the States. One is GSM, which consists of AT&T and T-Mobile. The other is CDMA, which consists of Verizon and Sprint.
The difference here is that how the phones operate and behave on each network.
A GSM phone identifies the subscriber (YOU) via the little chip called a SIM (Subscriber Identification Module). While the CDMA device uses a BURNT-IN, READ-ONLY ESN (Electronic Serial Number) to identify both the device AND the subscriber.
In certain parts of the world certain CDMA carriers DOES use removable subscriber ID modules, but they are not called SIM, instead they are called R-UIM (Removable User Identification Module). It behaves just like a SIM card on GSM phone but THEY ARE NOT INTERCHANGEABLE. i.e. you can't use a SIM card on a CDMA phone and vice versa.
Here's the tricky part. To lower the cost and minimize the amount of model variants of the iPhone 5. Apple decided to cramp BOTH operation modes into the phone, and only kept the LTE radio different due to carrier differences.
In the States, CDMA devices uses the ESN method for the carrier to identify them on the network. There no such a thing as a subsidy lock on a CDMA device as the identification module is permanently fixed inside the phone. Unlike GSM counterpart phones all you have to do is take the SIM card with you. With CDMA devices you can't, at least in the States.
When people stated that it's unlocked, that means the phone has no subsidy lock on GSM part. CDMA is a different story all together.
