If you have an X2 modem and call a Flex server, you will end up with at most a 33.6K connection. The same would happen if you have a Flex modem calling an X2 server. Finally V.90 was released which, instead of a company standard is an industry standard. Most ISP's in this area have upgraded their dialup servers to V.90. If you have a 56K modem that does not currently have V.90, you should check out your computer manufacturers website for a potential software upgrade.
Some modems can be upgraded by software, some require the modem to be swapped out.
Most upgrades to this standard are free. In our area of Wisconsin it appears to more have to do with the phone lines, as some phone companies haven't upgraded their systems, and many homes have older wiring that is just not capable of sustaining this level of communication.