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my %prefixes = ( '04025' = [ 'Region1, Region2, Region3' ],
                 ...
               );

my ($pref5, $pref4, $pref3, $pref2) = map { substr( $phone, 0, $_ ) }
                                          (5, 4, 3, 2);
...
                            substr( $phone, 0, $prefix_length),
                            substr( $phone, $prefix_length),
                      );