Hello, ​ I have a client that is interested in leaving Ooma, and would like to keep using their Ooma Branded (and firmware'd) phones with other providers. The bottom of the device shows that it's a Grandstream device, and that Ooma is the 'importer'. I've been able to gain access to the administrative WebGUI for one of them, and I can even get it to download configuration from my switch! The phone will not register however. It seems that it's running a custom firmware that Ooma puts on this device and some of that isn't/can't be programmed by my switch. I suspect I might be able to manually provision each phone (and each button on each phone), but that sounds not-great at best. ​ When I try to upload the current Grandstream firmware via the web interface to this phone, I get a Firmware Provision Failed message on the phone. ​ Entering in the [firmware.grandstream.com](https://firmware.grandstream.com) address (and HTTP) also doesn't seem to affect it. Has anyone been able to flash standard GS firmware on these phones? I called Ooma, and their overseas support said that "these phones should only be used with Ooma service". ​ Has anyone accomplished a firmware reflash with the stock firmware?