asterisk users - Sep 2008 - Dial function, and no telephone line fixed in the fxo port

Hi List;

First of all, how can I know that the telephone line is not fixed in the fxo
port?

Then, if the Dial function used to place a call via the zaptel (via the fxo
port), and no telephone line was fixed in the fxo, can I have any returned error
to know that the telephone line is not fixed in the fxo?

Last issue: if there any allarm (in any file, or via some script) to give notice
that the telephone line now is disconnected from the fxo port?

All of this because my customer always keep removing the telephone line from the
fxo and use it for some other purposes, we need to control this by giving
allarms, indications or something to let the use understand the reason of the
mistake, specially that people who remove the line, they do not say that they
removed it (they say, it is connected).

Any advise?
Regards
Bilal