All new smartphones that come in T-Mobile USA and Metro PCS networks have a new type of network blockade that is called Device Unlock App. If your phone has “Device Unlock” App installed, it can’t be unlocked by an unlock code. Once you will change the simcard with any another network provider simcard, it will not prompt for a network unlock code. If you insert an unaccepted simcard in this type of phones, the unlock request will be shown in this special app.
If you will launch “Device Unlock” App, you will find two options only : permanent unlock and temporary unlock. Once you will press the permanent unlock, the message should appear that the device is not eligible for unlocking.
From this service you can unlock these types of phones remotely. After unlock it will work with any network as you wish.
You may find these types of unlocking app in the following models: