Buy outright or Verizon "upgrade"?

My family's 4 iPhones are paid off and we use Verizon. I'm debating buying 3 new iPhones from Apple and just paying for the phones (less any Apple trade-in). The alternative is to finance through Verizon and while the phone appears to be "free," I'm pretty sure that (a) I have to change my plan or otherwise pay for the purchase price by dividing it over 36 months, and (b) I'm locked into VZW until the phone is paid off.

Am I missing something? The VZW finance option is an interest-free loan, but with the hassle of being tied to VZW (and the particular plan I have to agree to for the deal).