You're forgetting, or maybe just never used a modem (some people ask what the hell a floppy is), but the max speed you could squeeze out of a 56k was like 3/4kbps for any single download. That's if you were lucky. You would never, ever have transfered so much as 10gb in a month.
Things sure have changed. I remember praying to the modem gods that the connection wouldn't simply drop when downloading something as small as 200kb. The good ol' days -- you made every moment on the net count.
the 56k stands for 56KBit/s. What you were seeing was 3.5 KByte/s which of course is still way off the theoretical 7 KByte/s you could achieve with 56KBit/s.
If you only got 3 KBit/s over a 56K modem, your download-rate would have been 375 bytes/s - a third of a Kilobyte per second. That's a bit more than what you could have reached with a 2400 baud modem from the eighties.
You get to your 10 months result by dividing the 10 Gigs by 3Kbit/s, while you would probably have ment to divide by Kbyte/s
I never once saw more than 48kb/s on any 56kbs modem I ever used (as i recall there were two slightly different implementations at the 56kb/s level, but neither one ever achieved that speed in the real world).
With 8 bits per byte plus protocol overhead, a good rule of thumb is take the Kbps value and divide by 10 to get a realistic KB/s figure. It's been too long since the BBS/dialup days and I don't recall if some of the later modems implemented on-the-fly compression which would squeeze out even more bandwidth.
Things sure have changed. I remember praying to the modem gods that the connection wouldn't simply drop when downloading something as small as 200kb. The good ol' days -- you made every moment on the net count.
http://www.wolframalpha.com/input/?i=10GB+/+3Kbps 10 months.
Edit: What I just linked to above was incorrect. I should have used kilobytes per second, not kilobits per second.