I am trying to completely start fresh with an existing Yealink T48S phone. I remove the phone from the extension. Then I tell the user to factory reset the phone (press and hold the "ok" button). The user says it asks to reset, they click ok, and it reboots. The phone is behind a SBC. When the phone reboots, it looks fairly normal with a "No Service" blank BLFs, etc. In the web admin, on the phones page, I assign the phone back to the user's extension. Then then phone reboots.... and doesn't ask for a login (extension and voicemail pin). It just starts working. How can this be? When you factory reset the phone, doesn't it wipe it completely? How would it know the user's extension and voicemail pin? What am I missing?