Because when you buy an unlocked mobile phone, there is no mobile operator to subsidize the costs to the manufacturer and pay the full cost of the phone itself. At the point of sale and in signing a contract with a mobile operator that is understandable, but after that, a handset being open-minded can be a temptation about not impossible process. Your mileage may vary greatly with this solution, but in my case people in the street from my home were very responsive from the T-Mobile store and I do not think twice about letting me try out one of their SIM cards. On the subject of mobile CDMA and GSM, here in the US is still quite common, but for most of the rest of the world, GSM is the dominant mobile technology, and it seems that mobile technology is as a whole in that direction. If you can call the SIM card to another mobile operator on the phone, the phone is unlocked. However, if this is not possible, the phone is locked by a wireless service provider and you must talk to the wireless service provider whether or not to unlock the phone. On some phones you only need to extract the card. For others (such as iPhones), you need a paper clip or SIM removal tool that fits into a small hole next to the SIM slot. Adobe Logo Design Software. Cellular technology is a bit complicated and the transition to a single 4G standard has made things a bit easier, but a device between all four airlines in the US is still a bit difficult. You can do this by filling in the phone model, the network where the phone is locked and complete the email address. Submit the unlock code. If you want to know if your wireless service provider has kept its promise. To enable customers to unlock their phones, check the mobile number locking card to see how it works so far. A result of using a SIM card from a network other than the Android phone you are buying from. You can not call or use their services.