Because the discounts might vary from carrier to carrier, some people throw a fit when they can't get a "free" phone (under subsidy) and instead get the "free" phone from the other carrier. It used to be that Local Number Portability didn't exist, and if you switched carriers, you lost your phone number. Once that went away, the only thing keeping people chained to the network was the device lock. With that gone, the only thing keeping people with any carrier is the constant offer of discounted phones.
Although Wireless is most known for it, it also happens with Cable Television, and Wireline DSL service. Sometimes you only get a better deal by switching carriers every 2 years. Out here, if you want the latest TV/PVR box from the TV/Internet provider, you're almost required to switch every 2 years because owning the equipment locked to the provider (some costing nearly 1000$) is a rip off and you're better off renting the equipment and turning it in every 2 years when you switch. If you move to a city that doesn't have that provider, you can't use your equipment you paid for anyway.
