Similar to a host of other services currently available, you essentially go online to www.trade-in.vzw.com and enter in some information regarding your used or new phone. During the process, it'll ask specific questions like the condition of the device – whether or not it's working or perhaps damaged. From there, you'll eventually get an appraisal amount which would be sent to you in the form of a Verizon Wireless gift card.
Although some devices will fetch more money than others, an Apple iPhone 4 32GB version for example, will dish up approximately $212 – which can be seen as being pretty low, but then again, can be okay for some. If you do decide to send it, there is an option during the process which will allow for a pre-paid box to be shipped to you. Additionally, there is also an option to donate your phone to charity if you wish to do so.
So if you don't want to hassle yourself by putting up your phones on auctioning sites or even something like Craigslist, this may become especially useful to you.
source: Verizon Wireless