f, err := os.Open("cards.vcf")
if err != nil {
	log.Fatal(err)
}
defer f.Close()
dec := vcard.NewDecoder(f)
for {
	card, err := dec.Decode()
	if err == io.EOF {
		break
	} else if err != nil {
		log.Fatal(err)
	}
	log.Println(card.PreferredValue(vcard.FieldFormattedName))
}