@LaF0rge Thank you i will certainly poke around there.
Analog modems are available too however if you could make an ISDN service available via public network i would certainly _try_ to make it work just for the heck of it.
I have a DEC brouter90T1 hooked up via serial to a 2620XM that sports several ISDN BRI ports plus a Digitalisierungsbox smart in media gateway mode and two fritzboxen (pyur & o2) that are waiting to get put to use.