I have a phone under my ex girlfriends name with Verizon, needless to say she won't add me to the account as a primary person to change the contract so I'm stuck with a 2yr contact I can't afford, so I got at&t card and I can't get internet service!
at&t says Verizon has to unlock my phone, Verizon says it can't unlock my phone! I have at&t SIM card in it and get error message. Any clue on how to fix. plz help
You will need to add at&t APN into your phone settings and turn off Verizons. Go to Settings > More Networks > Mobile Networks > Access Point Names (APNs) and add a new one by hitting the "+" and call it AT&T. Use at&t APN settings:

Once you do this, you will be able to use your data to go online, otherwise you're stuck using WiFi.
I went into an AT&T store and watched the tech guy do this to my Verizon S8 phone so that it will work with AT&T. Just added AT&Ts APN and I was good.
Hope this helps.