If you can get the filter off - here are some wiring diagrams for phone jacks-
http://images.google.com/images?hl=e...-8&sa=N&tab=wi
http://www.naturalhandyman.com/iip/i...e/inftel1.html

or maybe the filter went bad

you could try a test with a regular dsl filter to see if the phone works normal then.

but you'd still have to get the wall filter off first

no little slots or ridges to pry it up ?

there has to be a way to get it off - because the repair guys would have to do it sometimes too.