maggioneato,
I've recently installed broadband and I've fitted a filter to each of my sockets (3 in total).
In two cases there is just a phone plugged in and in the 3rd case I've got the adsl modem and a dial up modem plugged in (dial up is just in case).
As long as you plug BT appliances into the BT sockets and your adsl modem into one of the adsl sockets you should be fine.
As far as I know all adsl/bt filters should be functionally the same.
Hope that helps, good luck.
dd
