We investigate what data loss on an iPhone shares with Apple and what
   data Google Android on a Pixelphone shares with Google. We find that
   even when minimally configured and the handset is idle both iOS and
   Google Android share data with Apple/Google on average every 4.5 mins.

   The phone IMEI, hardware serial number, SIM serial number and IMSI,
   handset phone number etc are shared with Apple and Google. Both iOS and
   Google Android transmit telemetry, despite the user explicitly opting
   out of this.

   When a SIM is inserted both iOS and Google Android send details to
   Apple/Google. iOS sends the MAC addresses of nearby devices, e.g. other
   handsets and the home gateway, to Apple together with their GPS
   location. Users have no opt out from this and currently there are few,
   if any, realistic option