Tried their higher tier services - they work great. But I don't need them. So I've been paying $0 in phone service for a few months now.
It is only limited by Sprint's 3G coverage, and if its available you use the 4G instead. They even have a nice $70 a year unlimited minutes and messages plan (same 500mb of data - I don't think their data rates are competitive at all imo, but then again no phone companies data rates are competitive unless you had exactly 7 people on a tmobile plan).
This is after trying out Tracfone, Republic Wireless, and Ting. It is really hard to argue paying monthly if you don't have to.
EDIT: Added that roaming onto Verizon is no cost for Ting.
Free is brilliant if there is a viable business model to make it pay.
A year later, they were still going, so I gave it a shot. I don't regret it. If the floor falls out, every sane MVNO in the US is Sprint based anyway and I can move my phone to any of them.
Edit: and a battery and a case...