D-Link D DPH-50U DPH-50U Quick User Manual page 28

If you are on a PBX, you may need to press a digit to get an outside line (i.e.
9). In this case you would enter 9,,,16175551212.
In order to forward incoming regular calls to a VoIP call, such as through
SkypeOut™ or to a Skype account, enter speed dial number (e.g. 77)
associated with the Skype User without the * key (as shown above).or enter
the SkypeOut™ number (e.g. 0016175551212).