No unauthorized users could touch the "customer list" machine, so there was no hacking it out of the software in a sensible sane way. None of the rituals in their little book come close to "dump database in CSV" and the thing is equipped with only a modem, a floppy drive, and a big ass tractor feed line printer they run the bills on.
But the "run the bills* ritual is one they have, and the printer connects to a parallel port, and I can with a little bit of bodge connect my little laptop to the other side of that parallel port... capture the "bill run", parse out the addresses, and finally emit their DB in a useful form.
Building that was actually fun, but then no one else could assemble the laptop stack to actually perform the procedure so I owned the entire operation for the short time it ran.
The ones the decide they didn't need and end up never using. All the wasted effort...
Also, I did some work with the GSMA (mobile carrier association) specitied SOAP based SMS api. That was exciting... Turns out different implementations of the server need different xml posted to them, even though they theoretically use the same spec. And then there's SMPP which is an open specification, except the standards org disbanded and shut their website, so you've got to find random PDFs out on the web somewhere.