This has been an ongoing problem, even with the new version of Wave:
Our VOIP backend is Sangoma FreePBX 184.108.40.206.
On an iPhone 6 running IOS 9, when the iPhone is idle and locked, the GS Wave softphone does not ring at all, and appears as UNREACHABLE in FreePBX but still listed with an IP address. I have tested this using 3G connection and LTE connection.
The issue may be with registration period timeout, but there is no way in GS Wave to set or check the registration period. I have tested with ZOIPER and does not have the same problem. Once the app stops receiving calls, the only way to fix the problem is to close/restart the app, even though Wave displays the green circle indicating it is connected to the SIP server.
I have also tested using Stun server and keep alive settings, and both have the same result.
When the app is first launched, it works fine, and if the phone is kept open, it works fine. But as soon as the phone locks, the app no longer receives calls. There are no problems making outbound calls.
Has anyone else had this problem on an iPhone 5 or 6?