When the DSL modem is on, the phone still acts up even on extensions that are well-removed from the modem.

Before my friend got DSL, she had a one-line phone jack that the fax and phone shared with a little Y adapter, the "splitter" above. This is just a hardware store phone accessory, not a DSL line splitter that the telcos install.

To use the DSL, we unplugged this adapter from the jack, plugged it into a microfilter and plugged that into a second adapter. The DSL modem plugs into the second leg of this second adapter., which plugs into the phone jack.