You cannot use it on any USA carrier. It is unlocked for use out of the country only.
Someday maybe. I know that T-Mobile and AT&T have limited use with certain devices. However they are GSM devices.
The iPhone 5s is unlocked for limited carrier use, on other networks.
If the phone isn't already unlocked for USA carriers, there isn't any way to manually unlock the country restriction.
The more recent models of 4G LTE smartphone offered by Verizon Wireless have been fully SIM unlocked including the country restriction. The only way to find out if the model you are interested in is fully unlocked is to insert another carrier's SIM card in the phone and setup their APN.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.