After a few days of seemingly bizarre network errors from some, but not all, apps, I realized my phone wasn't getting an ipv4 address. After three calls with poor tech support bodies who didn't know what an ip address is, I tried Sprint's chat support. I was surprised when they promptly told me that all internet data is now ipv6. However, they said they could do a workaround for me.
Moral, ipv6 is coming. Google says it is at 18% worldwide, and 34% in the US. https://www.google.com/intl/en/ipv6/statistics.html