This will create what you want:

  use XML::Smart ;
  
  my $xml = new XML::Smart() ;
  
  $xml->{phone} = '555-1234' ;
  $xml->{phone}{type} = 'home' ;

  print $xml->data ;
[download]

Output:

<?xml version="1.0" encoding="iso-8859-1" ?>
<?meta name="GENERATOR" content="XML::Smart/1.6.8 Perl/5.006001 [MSWin
+32]" ?>
<phone type="home">555-1234</phone>
[download]

See the method apply_dtd() in the XML::Smart documentation to apply automatically a DTD to all your tree.