Kernel Support

Make sure your kernel version is larger then 2.0.36 and supports the ISDN subsystem if not you must get a newer kernel and compile it to support ISDN subsystem and your ISDN card (for example: if you have Avm Fritz!PCI then choose Hisax support for AVM PnP/PCI (Fritz!PnP/PCI))
You can type: modprobe hisax type=XX protocol =2 to check if your kenel can load the ISDN subsystem. (if everything goes well, you might see one line or nothing...). You should replace the XX with your ISDN card type you can find list of types in: /usr/src/linux/Documantation/isdn/README.HiSax
Protocol=1 says you are using the card in euorpe and not germany.

Make sure your kernel version is larger then 2.0.36 and supports the ISDN subsystem if not you must get a newer kernel and compile it to support ISDN subsystem and your ISDN card (for example: if you have Avm Fritz!PCI then choose Hisax support for AVM PnP/PCI (Fritz!PnP/PCI))