This just randomly appeared in my settings menu about 30 mins ago. I called VZN support and they have no idea what caused it. Is my iPhone 4S now unlocked, or something?
It's nothing new. It's just that it's usually hidden. Nothing to worry about, you're phone is not unlocked. I get it sometimes on my Sprint 4S, but usually only after I restore / update. Don't worry about it.
I've always had this except on top it doesn't say "Carriers" it says "Network Selection". I think it may be for roaming because when I went to the states I was able to turn off that option and select a carrier manually, and with the option on the phone would just search and pick a carrier on its own.
I've had it since day 1, and like sviato it says "Network Selection" once I go into it. There's a separate menu for roaming, but I think this was added by Telecom here in NZ.