There are two types of 56K modem - x2 and K56flex. Try to connect to an ISP that uses x2 technology with a K56flex modem, and you won't get your speedy 56K connection. Our advice is simple, check which standard your ISP is supporting before you buy a 56K modem. Hopefully the distinction between x2 and K56flex will become irrelevant. If you're planning to buy a 56K modem in the near future, make sure it's one that can easily be upgraded to the standard once it's finalised.
Manufacturers often release updated versions of the software that controls modems.
If ISDN isn't for you, you might want to look at channel bonding. This doubles the bandwidth by binding together two modem connections over two phone lines. No UK ISPs support the technology yet, but some are considering it. Most email programs allow you to send and receive your email all in one batch in one online session. They also allow you to write emails offline.