I have successfully used on of these on e-smith 4.1.2. You need to configure the init string on the isdn adapter to default it to the correct parameters i.e. 64kbps single channel - so that when e-smith sends ATZ the isdn adapter initialises properly. You then just treat it (as far as e-smith is concerned) as an external modem.
Do a search on google and you should find the init strings required and how to configure - let me know if not and I will dig it out and send to you.
Regards,
Tim.