Carrier Services (https://play.google.com/store/apps/details?id=com.google.android.ims) Runs in the background. Play store description claims power savings in addition to the features, but I don't see how that could be the case. IMS(Ip Multimedia Subsystem) is an open industry standard for voice and multimedia communications over packet-based IP networks (VoLTE/VoIP/Wifi calling).
Phones target this application