I have the exact same modem, this is what i did to get it working:
Before doing this unplug usb from modem at the back to unload the windows drivers.
Log in as root
1. Go to this website http://eciadsl.flashtux.org/download.php?lang=en
and download the
eciadsl-usermode-0.8-1.i386.rpm , you can install this file by double clicking on it then typing in your root password. or use the command line, rpm -i eciadsl-usermode-0.8-1.i386.rpm.
2.Now as root from the command line type eciconf.sh , this will bring up the ECI linux driver configuration tool and change these settings:
Update provider= BT uk
Select modem = Bt broadband Voyager
Change your user name and password to the one you use in windows in this format:
(yourname = the one you used when regestering)
Leave the other settings alone for now and click remove dabusb and then create config, now click quit.
3. Plug in your modem again and from root terminal type /usr/local/bin/startmodem | tee log.txt and watch the output.
it won't connect properly but will give you your primary dns and secondary dns addresses, keep this terminal open and unplug you modem again, open another terminal and type eciconf.sh , now enter the primary and secondary dns addresses from the output in the other terminal and click create config.
4.Plug in your modem again and as root type /usr/local/bin/startmodem | tee log.txt . Watch the output and once it says connection successfull , try opening a web browser to see if you are connected or not.
If you dual boot with windows make sure you unplug your modem after using Linux for about 10-15 seconds to remove the linux drivers from memory or windows won't detect your modem.
p.s i am quite new to linux and i have found that i must be root to run these commands, su or sudo won't work, maybe somebody will know a way around this if it is a problem.
Hope this helps