Directly from a Verizon rep today:

With the EDGE program, you are basically paying the full retail cost of the phone, but it is broken up over the course of 24-months. There are no finance charges with this (that is with our Device Installment plan which is different). Once you have completed 6 months (currently 30 days due to the promotion) and paid off at least 50% of the phone, you can trade that phone in and get another new phone. It is really great for customers that like to get the newer phones when they come out.