您可以使用iOS VoIP推送通知来完成. VoIP推送使应用程序即使在后台也可以激活，并被用户强行杀死.所有语音和视频呼叫应用程序都使用此优先级推送服务.

You can do it using iOS VoIP Push Notifications. VoIP push enables apps to become active even in the background and forcefully killed by user. All voice and video calling application use this priority push service.

这里很棒 Apple语音指南IP(VoIP)***做法.主要用例之一–使用VoIP推送通知来避免持久连接.

Here is great Apple guide about Voice Over IP (VoIP) Best Practices. One of the main use case – use VoIP Push Notifications to Avoid Persistent Connections.

要使用VoIP推送，您必须连接 iOS PushKit框架.您可以配置您自己的服务器或其他第三方提供商.

In order to use VoIP pushes you have to connect iOS PushKit framework. You can config your own server or other third party provider.