I know to do it with Verizon I had to turn off my Samsung S4, call a number from another phone, enter some info, and restart my 6... worked fine after that. There were some instructions attached to my phone when I got it.
I have premire - I clicked the link in the order email to activate it. Entered the required numbers and then it said "pending" and that I'd get an email when it activated. Nothing for 1 hour. I rebooted and nothing. I called the support number, entered my phone # and it said it was now activated and to reboot. That did the trick.