i forgot to mention that as well as unplugging the telephone line, i also unplugged the foxtel[cable tv] digipath[tm] unit. that enables me to order pay per view shows via the remote control, and one or two other things. i didn't really give this much thought, i was solely concentrating on the 'phone line.
however, i've discovered that if i leave the 'phone connected and just unplug the cable from this unit that goes to the main 'phone socket, i can still achieve the faster adsl speed.
i'm sorry i didn't give you all the correct information earlier, i just didn't imagine that this particular cable would be relevant.