Examine if you really need to enter a 2-year contract.
Look at the Montly 4G plans. What are your needs - how many minutes and how much data do you need ?
I went with the 100minute/unlimited texting/5Gb plan for $30/mo. Even buying the phone up-front I'm saving a great deal over locking myself into a contract - a contract that wouldn't even give me what I actually wanted.
I made the mistake of going contract with Sprint on my first phone off of my family's the family plan. Overpaid for service I barely used. I don't see myself going back to contract plans - you overpay in the long-run - much more than if you just bought the phone and then paid a lower rate for the service instead of the hidden fee of paying them back for that "free" or "reduced cost" phone.
For instance, if I went with Verizon and paid $80/mo for their cheapest smartphone plan, that's $1200 more over two years than I'm paying now. Take away the $450 I spent on the phone - that's still $750. I could literally buy a brand new phone with THAT, even and two great-condition used ones. Maybe I'm a cynical jerk, but carrier subsidising is just a way to trick you into paying more money.