I had a patchset to make linux 2.0 / 2.2 talk PPP to several ports on livingston gear or itself. I got reports that it worked in some other situations; and there was an interesting bug report from an early version of Android that looked a lot like one of the failure modes i saw and never fixed in that code.

Best I ever did with that code was a bank of 8 ISDN modems to a PM3 that we did as a test at the ISP's office just to see how far it could stretch. 230kbps serial ports on an ISA bus.