Anyone have any idea how to make this work? I've flashed it to SIP but having issues. Seems like this phone is really tricky even with Asterisk but from what I can tell, on Asterisk only certain firmwares seem to work on it. I tried with 8-5-4S which seemed to have the best luck. It would show in 3CX that it was registered and if I called it it would receive a call (but not be able to answer it) but the phone would just say Registering forever or show an X over the line. I upgraded to 9.0.3S or something like that but now it doesn't even register at all. There's so many firmware versions and it's a major pain to keep changing them around so was wondering if anyone had any experience getting this to work?