you have to fart....         
 
change your phone number for thirty bucks............
take the phone apart   and put a silent mode switch in there...
record the modem sound   (squelching)   and play that back to them
so they think they have a fax number
disconnect your phone except when you really need it
download   the use over the net phone dialer app.
it can screen your calls and auto hang up for specific numbers