SL-009FI 62584 ADSL filter *new*

The ADSL filter enables the use of an analog telephone terminal (telephone, fax) in an ADSL connection. The ADSL filter is connected to the telephone socket of the ADSL connection. The telephone terminal is connected with the 3-pole telephone plug of the ADSL filter. The ADSL modem is connected to the filter's ADSL connector with an RJ11 connection cable. The ADSL filter is used in all parallel telephone sockets of the ADSL connection to which a telephone terminal is connected.

In short, if you have ADSL line and you want to use landline (phone) then you need this in between.