Here is how a Belgian ADSL connection looks like:
this is the general schema starting with the telephone line
Use the ADSL-filter for each telephone connection !
Insert the filter between the telephone socket and the telephone, the fax or the answering machine (see picture 2 and 3 below).
Note that the telephone wiring uses RJ-11 connectors.
Check out the Belgian ADSL forum for information on ADSL providers.