have a customer who has a DCS 408 and would like to set up a courtesy phone that dials a preassigned number when the handset is lifted is this possible

Simple answer is yes. Its called hot line or automatic line selection. That is however with a caveat. You are not in the US market and the programming might be a little different.

Nope, same I presume, hotline the extension and make sure to set the off hook dial timer to 0 seconds (default is 8 seconds for some reason).