I appreciate you reaching out to the community with this concern. The Pantech Caper is an excellent device and has a lot of impressive features. It's hard to believe that it's not a smartphone. Since you are interested in using this device on a post paid account, I have posted the requirement to migrate a prepaid device to post paid service. They are as follows.
May I ask have you attempted to activate this device to a post paid account? If so, what was the results? Please share so I can further assist.