Yes they do and don't they call it UTM service? Seems the phone was "recoded" to act like a VoWIFI phone and hands off to CDMA (sprint) when the threshold is hit. Problem is, I've not found any listings to what that threshold is. Re-associating with a cell tower is said to be seamless which tells me, it's in "standby" mode till it hits that magic number then it switches. Running in and out of your house could result in a dropped call.