I see that there isn't any phone load for the 7920 in the flash of the 540, but I do see it in the listed options for phones in CCA. I understand this was EOL a while ago, but will it work with the UC?
It will work with the UC. The 7920 firmware is not available in the software packs, but you can manually install the phone load on flash. Let me know if you need help with that.