>perl -wMstrict -le
"my @numbers = (
   '123-456-789', '123.456.789',  '123 456 789', '123456789',
   '999-999.999', '999 999-999', '999.999 999',
   '9999-999-9999', '99-999-99', '0123456789',
   '999999-999', '999.999999',
   );
 ;;
 my $diff = qr{ [-. ] }xms;
 for my $n (@numbers) {
   my $match =
     $n =~ m{ (?<! \d) \d{3} ($diff?) \d{3} \1 \d{3} (?! \d) }xms;
   print $match ? '  ' : 'NO', qq{ match: '$n'};
   }
"
   match: '123-456-789'
   match: '123.456.789'
   match: '123 456 789'
   match: '123456789'
NO match: '999-999.999'
NO match: '999 999-999'
NO match: '999.999 999'
NO match: '9999-999-9999'
NO match: '99-999-99'
NO match: '0123456789'
NO match: '999999-999'
NO match: '999.999999'