Maybe you're on your first phone contract or have simply never owned a phone out of contract, but I can say for absolute fact that you do not get any special treatment for owning your phone outright. The cost of the plan is a fixed amount, subsidized or not. If you bring your own phone you are only aiding the carrier hedge their bets by paying the same monthly rate as a contracted user but posing zero repayment risk.
That's true with Verizon, AT&T, and Sprint. But not T-Mobile. As soon as you pay for the phone, you're monthly bill goes down. Also, if you bring your own device, you get that dropped rate immediately.