I recently purchased some Yealink T42G Gigabit IP Phones from eBay. Upon connecting them to my IP PBX, I realized that they were flashed with a customized firmware designed for Fonality PBX.
Due to this customized firmware, I was unable to update the phone’s firmware.
I learned that you need a bridge firmware which allows you to remove the customized firmware and then update the phone with the latest firmware from Yealink’s website.
If anyone needs the firmware for Yealink T42G, please send me a message!