I have a stack (~10) PCI ISDN Cards from AVM, then are the "FritzCard PCI V2" series cards, so no in-built audio controllers, but as long as your machine is faster than a PIII then you can do it all in software.

I have used up to 3 of these stacked up in my Asterisk PBX to then connect them up to the phone lines for dial in & out lines.

Selling them for $10 each.  PM me if you are interested.