Correct me if I am wrong but if you previously if you purchased a Verizon phone it works on all carriers except Sprint. If you bought an ATT version then it would not work on Sprint and Verizon. Thats the change I am referring to, this year the ATT unlocked phone will work as the Verizon model and work on ALL carriers except Sprint.
Then the words you are choosing to use aren't what you mean.
An unlock means to SIM-unlock a phone for use on any carrier. Unlocks have nothing to do at all with the modem. Whether the modem is capable of using the frequency bands of any given carrier is a design thing.
You can have an unlocked iPhone that cannot work on one carrier or the other because of it's modem. It's still unlocked, but because of the modem it's incapable.
Conversely, you can have a phone that is capable, because of it's modem, of being used on many carriers. But because it's SIM-Locked it will only function on the original carrier until unlocked. Again, that has nothing to do with the modem.