I have seven phones (plus a Sky Box) together with a broadband connection. I bought a BT REN booster as I knew the max REN supported was 4 (and have potentially 9 if include Sky box and the ADSL modem).
Unfortunately, my ADSL router/modem periodically 'drops' its connection and this can be restored by disconnecting the REN booster (leaving only the broadband and 1 phone connected). Curiously, it can sometimes work happily for days with all the phones connected via the REN booster - but at other times just won't play ball when the REN booster is connected).

I was interested to learn about REN numbers. Do you think I can overcome the REN problem by switching off the ringers on my phones? (At least 2 of them have switches - and from what you say, the Sky box won't matter). If switching off the ringers will solve the problem, I could always buy one or two new phones with switchable ringers.

I was also interested in your comments about the microfilters. Does each microfilter take up some REN value? I currently have a microfilter on the main BT socket (which feeds my REN booster) plus also microfilters on each of the phone extensions. Might using just the one on the main BT socket help with the REN situation? (and would it still prevent the line noise for each extension)?
Many thanks.