(In case the phone is ever lost or stolen, so they can render it worthless)
Just curious.
My cheap phone and my no-contract service is very inexpensive, but if it was ever stolen, I could have the unused service balance transferred, and the phone would be rendered worthless to a thief.
I can see wanting to be able to sell or donate an old but still good higher end phone, and also why one might want to change service providers at will.
But doesn't this also make it easier for thieves to profit?
Your phone’s handset registers it’s “hardware” (usually referred to as an IMEI for most phones) every time it authenticates with a network (aka you turn it on, travel, etc). The phone company knows that IMEI belongs to you.
When someone steals your phone, you should immediately call your provider. They will basically “flag” that IMEI as stolen. Options at this point for the company range from sending its location data to the police, all the way to (most likely) simply not allowing that phone to register. In other words, turning it into a brick. Or, in your terminology, activating a kill-switch.
This it the case for all cellular phones from the fanciest smart phone, to the dumbest burner phone (which I proudly carry).