So where the splitter is connected to the phone socket, the phone line and the modem's ADSL line should be plugged. Or do I also need a filter on the splitter for the phone? As for the other sockets, I don't think I need to have filters on them. Isn't part of the problem the phone line is interfering with the ADSL? If it is, we only have one phone line, if you unplug that line, no other telephones work, which means it can't interfere with the ADSL. That phone line is connected to the splitter. I'm a bit confused. Please correct me if I'm wrong.