I was searching Driver Guide for good ISDN winbond driver. I've found two but they didn't work well. So I checked again our database and finally found actually working driver, which I submit here with best wishes for all.
The file is compressed RAR self-extractor with Win98/NT/2000 drivers (tested on Win98). ISDN line & card diag tools included.
Make sure you properly removed previous driver if installed.
/firstname.lastname@example.org >> chef.freeurl.com/