No. The socket plate is an 'instead of' option. It provides filtering at the socket, allowing you to connect all phone through it, filtered and running fine.
If you go for the ad-on filters, you need one for each ringing device. Remember the ADSL is fine with or without filters. The phones need the filters as they use a certain frequency on the line.
So you have both the phone's cable and the RJ-11 (PC) cable both coming out of your filter? It should work. Perhaps a bad filter. Just the one phone on the line or others? Wired bells count as ren devices too BTW.
I suggest you check out <A HREF="http://www.adslguide.org/" target="_new">this</A> site for more info. Check the FAQ section, and search the forum boards. Post there if you like. There's an extemely helpful mod there called Mr Saffron. What he don't know, you don't care about.
<b><font color=blue>~ <A HREF="http://www.btvillarin.com/phpBB/viewtopic.php?t=324" target="_new">My System Specs</A> ~<font color=blue></b>