I'm looking at our mobile install data and we have a few hundred thousand mobile app installs in the US. However, our analytics platform provides only IP4 address of each install -- however, I thought most US wireless carriers have switched to ipv6 -- how is it possible that all these devices have an IPv4 address?
IPv6 is not backwards compatible with IPv4, so to be able to reach any IPv4 network address, your device must have an IPv4 address as well, otherwise (simply put) the other end doesn't know how to reply to a the package.
So in essence, "doing IPv6" typically only means "being addressable with an IPv6 formatted address". If you would only do IPv6, you would only be able to communicate with other IPv6 devices. Including routers and the whole infrastructure underlying most part of the internet.