Как раз я про мессенджер который СОВМЕСТИМ с SIP, как клиентом, так и как транк.
И текстовые SIP Simple поддерживает, кстати.
Где тут совместимость только с собой вы увидели?
"У вас весьма плохо с фантазией."
LostSoul вы пока подучите матчасть для iOS, а на сегодня у меня лимит ответов как у новичка, закончился: https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/OptimizeVoIP.html#//apple_ref/doc/uid/TP40015243-CH30-SW1
Use VoIP Push Notifications to Avoid Persistent Connections
In the past, a VoIP app had to maintain a persistent network connection with a server to receive incoming calls and other data. This meant writing complex code that sent periodic messages back and forth between the app and the server to keep a connection alive, even when the app wasn’t in use. This technique resulted in frequent device wakes that wasted energy. It also meant that if a user quit the VoIP app, calls from the server could no longer be received.
Instead of persistent connections, developers should use the PushKit framework—APIs that allows an app to receive pushes (notifications when data is available) from a remote server. Whenever a push is received, the app is called to action. For example, a VoIP app could display an alert when a call is received, and provide an option to accept or reject the call. It could even begin taking precursory steps to initiate the call, in the event the user decides to accept.
There are many advantages to using PushKit to receive VoIP pushes:
The device is woken only when VoIP pushes occur, saving energy.
Unlike standard push notifications, which the user must respond to before your app can perform an action, VoIP pushes go straight to your app for processing.
VoIP pushes are considered high-priority notifications and are delivered without delay.
VoIP pushes can include more data than what is provided with standard push notifications.
Your app is automatically relaunched if it’s not running when a VoIP push is received.
Your app is given runtime to process a push, even if your app is operating in the background.
