On ADSL self install, the faceplate into your house will be carrying signals of both frequencies, so you need to ensure that the relevant devices are able to interpret these signals correctly.

You should install a filter on each telephone device that uses the analogue phone (low frequency signals). This means all telephones, fax machines, sky boxes etc will need to be attached to a filter.

However, your adsl modem is able to live quite happily with the signals that is transmitted on the lower frequency.

Some examples:- 

Example 1

Example 2