[kevin_nisbet]

Just a word of warning, long term this may not always be a safe assumption.

For supporting technologies like wifi offload, VoLTE, etc the phone can be told to tunnel traffic back to the carrier network, even when using wifi. This is to support features like using wifi to complete voice call's, but could be used for IP mobility as well (keeping you're IP address as you switch access networks).

I'm a bit rusty as I've been out of the industry for a year now and didn't work on this directly, so I forget how the phone get's this configuration. I think it might be an APN setting to connect back to the ePDG when on other access networks, but I could easily be mistaken.