FTSE Beater : I use BTopenworld and didn't have any problems with their USB modem.
However, I needed to be able to connect more than one computer to the internet. I had to dump BT's modem and I bought a D-Link DSL 504 combined modem/router (about £100).
More details on a thread called 'BTopenworld Broadband Question'. (sorry , i dunno how to put in a direct link to it from this message).
If u only need to use one 'puter and it's working fine at the moment, then an IT motto comes to mind 'If it ain't broke, don't fix it'.
HTH