D-Link DSL-100D Quick Install Manual page 3

Sharing your phone jack with the modem and another
device.
If you would like to share your phone jack with the modem and your phone,
then use a standard 2-line adapter.
Install the 2-line adapter into the wall jack.
Plug the RJ-11 cable into one adapter jack.
Plug the Line end of a "Z-Blocker" filter into the other adapter jack.
Plug your telephone devices into the PHONE jack on the "Z-Blocker"
filter.
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