I have a ZTE k88 from att&t I'm un saudi Arabia and mi sim card is STC Ir reconize the sim and carrier, i can send sms but everytime that i try yo call don't allow me to do ir. And i can't receive calls either. Why?

Screen on the K88 Tablet goes to sleep or to black in 5 seconds

I have been a long time att customer well beyond any contract. I wanted Mexico calling so was thinking of unlocking my phone and getting a sim card when I was on the phone. I got offered an upgrade to mexico calling and a free k88 tablet. I said I didnt want to get anything that added to my monthly

I have been sent same unlock code for two devices one has one more try other has 5 attempts do you need imie modles are zte k88,and on net it seem s you are having bad  problems with this modle

My trek 2 (that I bought a few weeks ago) is refusing to charge/turn on.I've tried holding down the sleep button, holding down the sleep button and the volume buttons. But nothing seems to work...

I know if i use a at&t sim card and connect to at&t network , then i can get the lastest version update via ota. but what if i dont use a at&t?  So i asked update files to ZTE USA SUPPORT TEAM because i dont use a at&t plans and then  they said that i should contact to AT&T support team because k88

When try to unlock "Looks like you upgraded your device..."Hello,Have bought 1 month ago the tablet, today I ve tried to insert my SIM card and worked it but I ve seen that it requires PIN-code.I live in the outside of USA and cannot find any At&t service, so I ve tried get my PIN unlocking code fro