I develop a SIP app in iOS and I would like to know if anybody have found a sip server that supports PushKit. It might be
- an existing sip provider
- an opensource sip server (eg asterisk) with this capability implemented
The SIP server doesn't need to support PushKit, this is something in iOS. There are 2 types of push notifications that the app can recognize and handle differently. Through the Apple developers portal you will need to generate a certificate type of Voip Services. Use this and the token while pushing and in iOS register and lookout for these. This site shows differences between push types: https://zeropush.com/guide/guide-to-pushkit-and-voip Apples best practices for VoIP: https://developer.apple.com/library/ios/documentation/Performance/Conceptual/EnergyGuide-iOS/OptimizeVoIP.html
On your SIP server, you will just need to send a push notification on an incoming call. If you use Asterisk you can use AGI so you can perform the push in whichever language. I've always just use APNS but there's a bunch to choose from like AWS, Urban Airship, Onesignal.
Urbanship confirmed that they would not support voip push in the near future (at the end of 2016). Finally, I found I can just use houston to send voip push. From my experience sending voip push and apn push are just the same from our side, e.g. they send to the same apple server, so I guess apple server will differentiate them based on their tokens and give voip push a higher priority.