ISDN menagement

I have tried many linux distros and now settleted with knoppix, but the only thing that keeps me from a total switch to linux (leavingthe dual boot with window) is , THERE ARE NO ISDN MANAGEMENTPROGRAMS FOR LINUX (ANSWERMACHINE THAT RECEIVES FAXES AND VOICE CALLS EN PROGRAMS
TO EASY SEND FAXES , I MEAN PROGRAMS WITH NICE AND SIMPLE GUI FRONTEND THAT ALL PEOPLE CAN USE)
I EVEN BOUGHT AN EXPENSIVE AVM FRITZCARD FOR THIS BUT NO LUCK WITH SETTING UP VBOX OR CAPISUITE ETC...
I THINK MANY PEOPLE ARE WAYTING FOR THIS ,SPECIALY IN EUROPE.