ISDN Dialup

This may sound like a stupid question, but I’ve never used ISDN before. Is it possible to have an ISDN line into the mikrotik to answer just standard analog modem connections? I’m looking for a cheap way to get a 56k connect into a Mikrotik box with only 2 lines or so. I have some USR I-Modem’s here that claim to support ISDN aswell as V.90. Would this give my clients a 56k connect into the box?

Thanks

Nik