After struggling for some days now setting up an ISDN connection to my ISP I
finally discovered that the ISP changes the gateway with every dialin.
German T-Online or Austrian AON at least do so. I verified it by connecting
from a Windows box and got a different gateway anytime I connected from
I4B and card are setup and dialing works. Also isdnd.rc doesn't report
errors. But the adapter can't establish the connection after dialing. At
least I know why now (hopefully).