That is unlikely, the relevant standard is V.90: http://en.wikipedia.org/wiki/V.90_(recommendation)

Only downstream was 56.6k PCM, upstream was 33.6k analog-modulated, so two consumer modems hooked together would only be capable of 33.6k.

There was a later V.92 standard that improved upstream speed, but is was a bit wonky as it sacrificed download speed to do it, I'm not sure how much it was really used.