Phone data transfer above 52k is impossible. It is a modem will never connect at 56k! The velocity factor of a phone line is the culprit along with interference. So remember a 56k modem box is lying!
Whoever told you that was full of crap. It is very possible to connect at speeds higher than 52k, and in fact, the highest possible speed to use on a Dial In modem is 112k. There is a technology called 'compression' that will allow you to effectivly double your connection speed. However, compression is expensive for ISP's to use effectivly, so most use very little compression, if any at all.
I just got on cable yesterday, but before that, I had dialup that would connect at anywhere from 24.4k to 28.8k. Compression kept my connection above 14k, which is all that these phone lines support. =\
My cable, on the other hand, is capped at 256kbps, but I'm getting 30 kbps right now. =\
Niku san wa tomodachi desu.
~Chi san