# writing $line to the appropriate file for $callid. 
# Filename is assumed to be "log.$callid" and is opened if not open
if (not exists $filehandle{$callid}) {
  open(my $fh,'>','log.'.$callid) or die $!;
  $filehandle{$callid}= $fh;
}
my $fh= $filehandle{$callid}; 
print $fh $line;