Soon, with the collaboration of unmaintained, a major update to S1P will be coming out to help with the problem. New features include operation as a daemon (so calls can be received anytime the phone it booted and lipstick is running), registration persistence controls, decoupled UI, better contacts support, early G722.1 codec, L16 codec, network change detection and registration, SIP over tunnel, early SRTP and TLS, TCP mode, early SMS/MMS messaging, UI improvements, independent controls for plugged headset. After that will come G722.2 codec, hooking into the SFOs phone UI (similar to yotogram), graphical logging and provider services available over SIP. IAX2 won’t be supported, most likely unless someone wants to write that module.
Around the same time, I may consider release some of my SFOs patches for animated themes, squared and tight UI elements (like Windows Phone), network connection persistence and resolution, camera functionality, Windows Phone like volume controls, animated gifs and webm in gallery and so on if there’s interest. I don’t use patch manager though- I quite literally patch the OS at build time. Zero interest in building a million packages. I should also add I only develop and test on the XA2 Ultra, 10 ii and Lumia 950XL.