Verizon phones are all unlocked.
insert the the new SIM card and restore to factory with iTunes.
if the phone is not blacklisted, it will say itis unlocked.
( find my iPhone has to be turned off so you can activate with iTunes and your account.)
Verizon iPhones 5 and above are all unlocked when bought.
To get this message:
1) it is not really a Verizon iphone
2) the SIM card is defective
3) the phone is reported lost, stolen, or contract terms not completed and the phone is black listed.