All the native Android/iOS push notifications are done by Groundwire SIPIS servers in the background. App doesn't need to be running at all.
So effectively the call registration is done like so:
PSTN/Whatever ------>Sipgate---->Groundwire SIPIS------>your smart phone
..........................................----->N300A------------------>your DECT handsets
The SIPIS servers keeps the registration alive with Sipgate servers, for calls to your smartphone.
Because there are effectively 2 simultaneous SIP registrations (one for Groundwire and one for Gigaset N300) at Sipgate then inbound calls are alerted simultaneously on both streams.
Edited by Pheasant (Fri 15-Oct-21 18:24:02)