I really want an iPhone but already have a plan?

So, I really want an iPhone, either a 4S, 5, or 5S, but I already have a plan with Verizon so it'd be really expensive. My upgrade isn't up for about a year and a half, a little less, and I don't want to wait that long. I've looked at eBay, but I really want a NEW iPhone, so I have the warranty and everything in case it breaks. Is there something where I can pay for the PHONE (NOT the plan) over time? Like monthly payments? I've looked online and all I've found is ".eu" sites that do that. Please help!

Added (1). The phone I got from Verizon with my last upgrade is lost.

You might want to call Verizon and ask them or go into one of their stores. I don't know for sure but it would seem if you agree to another contract with the iPhone and return your current phone they might be willing to do some sort of deal. That would be the only way without damaging your credit by breaking the current contract.

This "was" by far the cheapest plan available and it includes iphones. As always, make sure they have good coverage in your area or the main areas you travel between.
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Starting on January 11, 2013 in more than 2, 000 Walmart stores and online at Walmart.com, customers now have access to the iPhone 5 and iPhone 4 on Straight Talk's $45 no contract unlimited talk, text and data plan. To make this offer even more affordable, Walmart will be offering customers who purchase the phone in the store, a no interest fixed-monthly payments special financing offer for only $25 a month with a Walmart Credit Card.