PHONE_X
[
VLIB_PHONE_EXTENSION:z {<choice $z>}
]


VLIB_PHONE_EXTENSION (
  ?extension
  VSUB_NATURAL_FOUR_DIGITS_EXT:n {return($n)}
)

VSUB_NATURAL_FOUR_DIGITS_EXT [
  ( VSUB_DIGIT_STRING:a 
    VSUB_DIGIT_STRING:b 
    VSUB_DIGIT_STRING:c 
    VSUB_DIGIT_STRING:d 
  ) {return(strcat(strcat($a $b) strcat($c $d)))}
  ( VSUB_DIGIT_ONE_THRU_NINE_STRING:n
    thousand
  ) {return(strcat($n "000"))}
  ( VSUB_TEEN_STRING:n
    hundred
  ) {return(strcat($n "00"))}
  ( VSUB_DECADE_STRING:a VSUB_DIGIT_ONE_THRU_NINE_STRING:b
    hundred
  ) {return(strcat(strcat($a $b) "00"))}
  ( VSUB_NATURAL_TWO_DIGITS_STRING_EXT:a
    VSUB_NATURAL_TWO_DIGITS_STRING_EXT:b
  ) {return(strcat($a $b))}
]

VSUB_NATURAL_TWO_DIGITS_STRING_EXT [
  ( [ oh zero ]
    VSUB_DIGIT_STRING:a
  ) {return(strcat("0" $a))}
  VSUB_TEEN_STRING:n {return($n)}
  ten {return("10")}
  VSUB_DECADE_STRING:t {return(strcat($t "0"))}
  ( VSUB_DECADE_STRING:t
    VSUB_DIGIT_ONE_THRU_NINE_STRING:u
  ) {return(strcat($t $u))}
]


VSUB_DIGIT_TWO_THRU_NINE_STRING [
  two {return("2")}
  three {return("3")}
  four {return("4")}
  five {return("5")}
  six {return("6")}
  seven {return("7")}
  eight {return("8")}
  nine {return("9")}
]

VSUB_DIGIT_ONE_THRU_NINE_STRING [
  one {return("1")}
  VSUB_DIGIT_TWO_THRU_NINE_STRING:n {return($n)}
]

VSUB_DIGIT_STRING [
  [ zero oh ] {return("0")}
  VSUB_DIGIT_ONE_THRU_NINE_STRING:n {return($n)}
]

VSUB_TEEN_STRING [
  eleven {return("11")}
  twelve {return("12")}
  thirteen {return("13")}
  fourteen {return("14")}
  fifteen {return("15")}
  sixteen {return("16")}
  seventeen {return("17")}
  eighteen {return("18")}
  nineteen {return("19")}
]

VSUB_DECADE_STRING [
  twenty {return("2")}
  thirty {return("3")}
  forty {return("4")}
  fifty {return("5")}
  sixty {return("6")}
  seventy {return("7")}
  eighty {return("8")}
  ninety {return("9")}
]

VSUB_TEEN [
  eleven {return(11)}
  twelve {return(12)}
  thirteen {return(13)}
  fourteen {return(14)}
  fifteen {return(15)}
  sixteen {return(16)}
  seventeen {return(17)}
  eighteen {return(18)}
  nineteen {return(19)}
]

VSUB_DECADE [
  twenty {return(20)}
  thirty {return(30)}
  forty {return(40)}
  fifty {return(50)}
  sixty {return(60)}
  seventy {return(70)}
  eighty {return(80)}
  ninety {return(90)}
]