Although Android Nougat and even Android Oreo are Samsung Galaxy phones, there still many devices are running on the Android versions: 4.x.x to Android 6.x.x Marshmallow. If some of you here are using a Galaxy phone provided by the Sprint carrier and are still in contract plan, here is the step-by-step guide to unlock your Sprint Galaxy S6 and other phones for free.
Note: This method is applied to the devices running Android 4.x to Android 6.x. The higher versions are not tested.
The process is not complicated, so you can follow it easily.
Also read: How To Unlock SIM Of Sprint LG G6 & LG V20
How To Unlock All Sprint Samsung Galaxy S6 And Other Devices
- First, you need to root your device and install the superuser The process depends on your device, so you can search on Google to root your phone.
- Now, download and install GTUpdate2_v3.1.8.apk but don’t open it yet.
- Install GTv3.1.5.apk and launch it. If you see an update window, tap on OK
- Next, launch GTUpdate2_v3.1.8 app, choose Update. Once done, reboot your phone
- After the restart, relaunch the GTv3.1.5 app and press on Unlock
- Now, you have to enable GCF mode. These following steps are very important, so you should do carefully.
- Launch phone dialer app, and dial *#0011#. Wait for a moment and then press on Back
- Go to Key Input and type Q and enter
- Head into Key Input again and type in 0000. Wait for 20 seconds
- Then, go to UE Setting & Info >Setting >Protocol >GCF and choose the top option in GCF 
- When you see the “success” popup, reboot your phone
That’s all! You have now fully unlocked your Sprint Samsung Galaxy phone. Simply set APN if you want to use 3G or 4G