You found this site by googling and have a phone that is locked to a network and want to unlock it. However, you do not know exactly what involves decoding and if you really need it.
In general, mobile operators sell phones locked, each in its network. Even if the phone is bought ‘over the counter’ (without subscription), that does not mean it is not network locked. At the time of purchase you can ask the seller (he is anyway obliged to inform you) if your phone is locked or you can check it yourself.
How to check if your phone is locked in one specific network and must be decoded to be used with any sim? Simply: insert a SIM card from any network other than wich you suspect that phone is locked. If you can call anyone then cell is not blocked. If you have no signal or tells you that you have an unsupported sim or ask your insert direct network code, then you got the answer: to use the phone with that sim (or any other sim) you need unlocking code.
Phone unlock can be done by connecting it at an interface or generating a code based on IMEI. There are some phones that, for unlocking, you just need the brand and IMEI. For example, any Huawei (here enter and Vodafone 858 Smart wich is Huawei U8160 or Orange Stockholm wich is Huawei U8180) is decoded using only IMEI and it does not matter the model, country or the network in which it is locked. For other models, you not need the country or network only the IMEI and model (any LG or any Samsung). For some models of AT&T you need PID (Provider ID from phone label under the battery). For Blackberry are required: IMEI and MEP or PRD (PRD is on the phone label). At Nokia: country and network (no matter the model) and at iPhone: IMEI, country and network. At iPhone is required also to know if the phone is in the blacklist or not (you can find this this service on this site).
Based on the information that you enter in the program, the phone enter in work and will receive a code that will need typed in the phone. Depending on your phone model, you will receive free assistance on how and where to put this code. The exception to entering the code into the phone is the iPhone which has a different procedure completion. Here you see how to finish the iPhone unlocking.
Procedure to insert the code in phone does not damage it, its software or hardware is not affected in any way. Phone functioning does not change, will work just as before decoding. The only thing that will change will be that the phone will behave just like any other new phone purchased unlocked in the network. You can use any sim card in it from any network.
Is it legal to unlock your phone? After you bought it the phone is in your property.
From that point you can do anything you want with it. You can use it locked in the network where you bought it, you can drop it in an aquarium to test whether can swim with fishes or you can enter by typing (when asked network code) the code received from generator (which is unique to each phone) code that will free it from the network in which is locked. You can try random codes on it … who knows? If you were lucky in the lottery you might get lucky and with decoding. We do not recommend typing / using codes already listed on various forums.
Regarding US citizens (or persons resident in the US), they should know their law no longer prohibited the phone unlocking without the consent of operator (it is the 2012 law that was abolished in the 07/25/14 by President Obama).
Is the warranty lose if you unlock using code? You will get different answers depending on which camp asked. Mobile operators, wishing to keep their clients in the network, will tell you that, of course, you lose the warranty in case of ‘unauthorized unlockings’. It is possible to lose it if you try a service to reprogram or try who knows what ‘doubtful’ methods that would change in any way the software or physical part of the phone. In these cases, your phone will not be in the condition it was delivered new. Regarding unlocking using network code asking manufacturers responded: ‘WARRANTY DOES NOT LOSE’ using this method. No the operators have made those phones but manufacturers. Furthermore, it is the method by which mobile operators unlock phones shipped: will deliver your unlock code that must be typed on the phone.
Any unlocked phone can still be used in a network which was initially locked.