Question about smart phone plans

[Spork1111]

The contract on my family's phones is about to expire and we're looking into getting new ones (the S6, if that matters). The last time we got phones, the only option was to get a 2-year contract or buy the phone outright. Now, every carrier is giving a "$0 down" plan. However, for Verizon's (the carrier we've decided on) $0 down plan costs exactly the same per month as the 2-year contract with 3 lines; this means that in the long run, the 2-year contract is more expensive (by ~ $700) because of the extra amount you paid upfront. From what I can tell, it's a similar story for every other major carrier.

 

My question is what is the deal with these $0 down plans. Logic would dictate that getting anything for free initially should cost more in the long run than if you paid for part of it upfront, but my research so far has suggested the opposite. I don't believe that the carriers would give you the phone for cheaper out of the kindness of their hearts. What's the catch?

[Guest]

I'd assume it's a marketing strategy due to ever increasing competition. 

However if I were you id ensure I had a long hard look at the terms and conditions page, like you say it does sound a little too good to be true. 

@Spork1111