I have a client with a Cisco UC520 system that I would love to convert over to 3cx. The client has quite an investment in Cisco phones, so if possible, I'd like to keep them, and change them out when necessary. I have a few questions for those who may have experience doing this already. I have a 7941 phone available for testing. From my research, a firmware file has to be uploaded to the phone using DHCP to point to a TFTP server. Where can the firmware files be obtained? Is it possible to revert the phone to it's original firmware when done testing? Is there a way to backup the current phone firmware? Are there any compatibility issues to watch out for? Is there any functionality lost? Do the sidecars still work as before? Thank you for your help in advance.