Got a question to ask. With Unifi, can it be configured using the existing phone socket in the wall?

My question is what is the solution if i want to use the phone for upstairs and downstairs? Coz if the phone signal is transmitted from only one source, either upstairs or downstairs, im afraid the reception will be weak.

My Unifi phone regularly does not work (getting engage tone calling out or in). Everytime I complain i was asked to restart the BTU. This is not the solution as it happens daily or 2 days once (only lately facing the phone problem). How can i get TM to rectify this?