The math here is incrediy simple, and it's clear you didn't do any of it other than thinking "Oh HURR DURR the unlocked iPhone costs more so u not saving any money."
Using 1st grade math, let's see how this pans out with AT&T for the next 2 years if I early upgrade on the 21st:
$449 iPhone + 24($39.99 rate plan + $19.99 unlimited text + $29.99 unlimited data) = $2608.28 I'll have spent over the next two years
Now let's see what happens if I go with the ETF and the unlocked unsubsizdized phone and go with T-Mobile:
$649 iPhone + $225 ETF + 24($69.99 unlimited talk, text, data) = $2553.76
In my case, it would actually be even lower because I'm joining back into my T-Mobile family plan
+$5 a line and $20 for unlimited data for 24 months is $600 so I'm not even near that $2553.76 price tag. It's actually going to be $1474.
As you can see, you can't just go "derp unlocked iPhone is costs moar so u not save the money u idoit looool"
While I'm on your side in this discussion, I do think it's proper to include the cost of another iPhone in 12 months when you do the math. At least thats what I'm doing when I do the math. I want a new phone annually so that price must be factored in for both carriers.