Earlier quoted context omitted.
But you're missing an important point: If you own your phone you can get much cheaper 'SIM only' deals with the mobile carriers, meaning that over your 1-2 year contract, you'll pay far less. Getting a new phone as part of a 'subsidised' contract is effectively borrowing money to buy a phone. Your loan repayments are the monthly fee. If you have the cash, buying the phone up-front is almost always cheaper.
Not the biggest U.S. mobile carriers. AT&T and Verizon have awful BYOD plans, as I understand it. I'd be thrilled to find out I could do better than my grandfathered AT&T unlimited plan (two phones, 5GB/each before throttled, $120/mo.), but keep their network.
It's absolutely cheaper to buy devices outright here.
Example of Three's One Plan for a 32GB 5s (£):
24 mo contract
Device 99
Plan 46
24 mo total = 1203
12 month contract + BYOD
Device 629
Plan 15
24 mo total = 989