Yup- and this is key.
You didn't have a choice before, at least not with the big carriers. They were going to take you for a full subsidy/installment/whatever phone plan,
whether or not you reaped the rewards of it. As such, it was silly to not sign a new contract and pay a couple hundred for a new $800 phone every 2 years.
Even back into the turn of the century, if you bought an unlocked phone off eBay, you were paying full whack for your rate plan, even though you didn't use a subsidy. I even had Cingular once try to tell me I was under contract, simply because I had signed up less than 2 years ago -- even though there was no contract (I paid for my own phone).
Then a couple of years ago, they started offering "BYOD" pricing plans, so I paid my $300ish ETF, got my iPhone unlocked, and "saved" $15/mo. It was roughly breakeven.
Now I just pay full price for my phone if and when I want a new one. It helps me recognize the full cost of what I'm buying, and it means I'm not tied to a carrier.