Will iPhone 6 cost you $649 over two years?
Verizon Edge is a program that provides you the flexibility to upgrade
  early, and pay for your device over 20 months rather than paying for
  it all upfront. You’ll make a monthly payment until your device is
  paid off.
  
  After 30 days, if you’ve paid at least 60% of the Edge device,
  you’ll have the option to Edge Up to a new device without any upgrade
  fees.


What does it mean?

You will have a 2 Years contract with Verizon and have to pay the additional Verizon service costs (phone+Data). Now each time you Edge up to next phone the clock starts all over again. (2 Years contract).

The only benefit is you do not have to spend the cost of the iPhone up front, but over 2 Years, and the ability to get a newer model.

For Verizon you will pay >$60/M for network services. With some other providers you will pay $40/M for about the same services.  Difference of 720/480 is $240 per Year that you pay more.

So you actual cost after 2 Year with Verizon is 649+720+720 =$2089, while direct buy will cost you 649+480+480= $1609.