clubman, no i've only installed a DSL splitter/microfilter on the main incoming line. From the exchange side prior to going to the splitter/filter the phone line does branch off around the house to various extensions, one of which does not have a phone connected. Another phone has a filter installed on the line and is very noisy! This phoneline connects back to the exchange side of the original filter - should it be the other way around - i.e. Should i have the DSL splitter/filter connected to the exchange directly and all further extensions connected to the phoneline side of the DLS splitter? hmmm