alright since everyone has just said no ( including me ) lemme clarify this to u
as stated above by mario the pc detects it as a lan device
hence it has no drect access to your telephone line
APART from this if u realise isp's ( atleast some ) install a sort of splitter with ur modem
one line in
one phone out
one modem out
this is not simply so u have a parallel line
this splitter also has a filter in it which segregates the data channel and voice channel from ur telephone line
since adsl modems tend to make a high pitch noise this is a good idea obviously.
atleast thats what it says in the theory of dsl

so i guess these 2 points should be enough for everyone to understand as to "WHY AN ADSL MODEM CANNOT BE USED TO ACCESS PHONE LINES ( to make calls, dial up, fax etc. )" and as to "WHY A DIALUP MODEM CANNOT BE USED AS AN ADSL MODEM "