[SR-Users] Calling a mobile SIP client, which needs to update the registration

Hi everybody, I am trying to call a sip client on a mobile cellphone, which is registered fine at my Kamailio instance. Everything is working fine if the phone is awake and the mobile app is not sleeping (e.g. energy saving by OS). If the device is sleeping, the cellphone gets a wakeup request call via apple push kit and wakes the app. Currently my app is doing a Register after each wakeup, because the device does not know if the cellular network changed (external IPv4 address with Carrier Grade NAT). At this point an incoming call already got routed to any existing user registrations in userloc db. In this case, if the cellular provided network address changed, the sip client on the device won't receive any invite of this last call. Instead all last known Contact-URIs are tried to be called until this sip invite times out because no response message is received back in time. I tried to delay the incoming invite message, but this doesn't seem the right way to go, since I can't know if the mobile device is actually reachable and this method would potentially delay every call. What is the best approach to solve this issue? I am looking forward for any comment or suggestion. BR, Henning