$.validator.addMethod( "phoneNL", function( value, element ) {
    return this.optional( element ) || /^((\+|00(\s|\s?\-\s?)?)31(\s|\s?\-\s?)?(\(0\)[\-\s]?)?|0)[1-9]((\s|\s?\-\s?)?[0-9]){8}$/.test( value );
}, "Please specify a valid phone number." );