i was afraid you would say so. anyway, if anyone else can provide some hint, I’d be very interested.
e.g. at h-node [1] there is one modem listed to work with trisquel. it is a pci card, but actually i do not understand who is the manufacture and where i could buy it.
[1] http://h-node.org/modems/view/en/458/Xilinx-Corporation-Device-0300