I don't know, it looks like paying the EFT and switching costs just as much over-time as staying with AT&T and paying full-price for an iPhone every other year (which qualifies you for the $199 upgrade rate every other year).
Doing the AT&T yearly "$250 early upgrade" looks to cost the most money!!!
If you look at these three scenarios...
AT&T model 1: (paying the early upgrade fee every year)
Year 1: $199
Year 2: $199 + $250 early upgrade fee
Year 3: $199 + $250 early upgrade fee
Year 4: $199 + $250 early upgrade fee
Year 5: $199 + $250 early upgrade fee
------------
$2245
AT&T model 2: (alternate paying full price every other year)
Year 1: $199
Year 2: $549 (don't do an early upgrade, pay full price)
Year 3: $199 (since you didn't do an early upgrade the year before, you qualify for this price)
Year 4: $549 (full price again)
Year 5: $199 (you qualify for this price again)
------------
$1695
Switching to Verizon
Year 1: $199 (AT&T)
Year 2: $199 (switch to Verizon as a new customer) + $225 ETF fee to AT&T
Year 3: $549 (they don't offer an early upgrade price)
Year 4: $199
Year 5: $549
------------
$1695