[72deluxe]

VoWiFi for LTE is what carriers (in the UK at least) try to encourage if you have poor signal at home. It still relies on your SIM being in the phone and actually makes a L2TP or SIP connection through to the carrier's server. I know because I disabled all these NAT passthroughs on my router and VoWiFi didn't work at all for me on EE with an Android phone (but did for my wife with her iPhone on Virgin). So you can still be tracked since the connection to the carrier's server requires an identity - it won't carry calls for just anybody!