If you decided to use the 1st solution, you should get javax.comm package and RXTX program  (This is a serial port driver for linux), then do some configurations that are described at www.rxtx.org.
If you decided to use the 2nd solution, the bash script function below converts your .pdf files to some .g3 fax pages which can be sent by mgetty.

convert()
{
 # Converts a pdf  file to g3 files
 if [ $# -lt 1 ]
 then
  return 1
 fi
 pdfname=$1
 bnm=`basename $pdfname .pdf`
 gs -r204x196 -dNOPAUSE -dBATCH -sDEVICE=tiffg3 -sOutputFile=${bnm}.tif $pdfname
 tiffsplit $bnm.tif _$bnm
 rm -f $bnm.tif
 for i in _${bnm}*tif
 do
  echo "tiff file : " $i
  j=`basename $i .tif`
  tiff2ps $i > $j.ps
  gs -r204x196 -dNOPAUSE -dBATCH -sDEVICE=pbm -sOutputFile=$j.pbm $j.ps
  pbm2g3 $j.pbm > $j.g3
  rm -f $j.tif $j.ps $j.pbm
 done
 return 0
}