// Work phone number for John Smith

SELECT ?telephoneNumber
WHERE (?person, <vCard:FN>, "John Smith") ,
      (?person, <vCard:TEL>, ?tel) ,
      (?tel, <rdf:type>, <vCard:work>) ,
      (?tel, <rdf:value>, ?telephoneNumber)
USING
  vCard FOR <http://www.w3.org/2001/vcard-rdf/3.0#> ,
  rdf   FOR <http://www.w3.org/1999/02/22-rdf-syntax-ns#>