You can sim unlock it, however since it's branded by ATT you cannot unlock bootloader on their software variant. root not possible either without serious side effects. if you want root go with Tmobile.
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You can download it as APK long as you have developer options enabled. Google tv plus.apk download it. then go into your phone, settings , about phone, tap build number 8, then go i to developer mode, enable unknown sources. your download with then install when you go back and click on it from the drop down menu.
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here you go to Settings > Apps > Show system Apps (click on the 3 vertical dots upper right of screen) > Smart Call > Storage > Clear Data and Clear Cache. Restart Phone
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a failing capacitor or buffer? Somethings up with the motherboard for sure on this if thats all its doing. A loose and or shorted component.
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