Yealink Factory Reset for T46S: hold down OK button until it prompts for factory reset. Yealink unknown admin password after factory reset or it auto provisions after factory reset: disable the Internet connection on the network that the phone is on, do a factory reset on the phone, when it comes back up the login will be admin/admin. Use your PBX to provision it, normally this will be a URL from the PBX that you will put in the phone webUI at Settings -> Autoprovision -> Server URL. If you factory reset the phone again it will go back to the original provisioning setup so you'll have to do this again. What we do on our network is to allow only the 3CX server internet access (via zoned firewall rules), the Yealink phones can only communicate with the 3CX server itself (as they are in the same zone) and they can make DNS/NTP queries to our domain controller (this is in case these device are every compromised or have back doors...)