If you have a list of 500 leads stored in a JSON file from a web scraper or a custom app, you cannot simply "open" that file in your iPhone's contact list. You need a converter to translate that data into a language your phone understands.
The ability to manually map fields is the difference between a successful import and a mess of "Unknown" contacts. Step-by-Step: Importing Your New VCF to Your Phone json to vcf converter
BEGIN:VCARD VERSION:3.0 FN:John Doe TEL:+1234567890 EMAIL:john.doe@example.com ORG:Acme Inc. END:VCARD If you have a list of 500 leads
vcf_writer.close()
// N (structured name) if contact.lastName or contact.firstName: last = escapeVcf(contact.lastName or "") first = escapeVcf(contact.firstName or "") vcfString += "N:" + last + ";" + first + ";;;\n" " + first + "