functions.php

<?php 
/**
 * Add vcard to upload-safe files
 */
add_filter('upload_mimes', 'custom_upload_mimes');
function custom_upload_mimes ( $existing_mimes=array() ) {
	$existing_mimes['vcard'] = 'text/vcard';
	$existing_mimes['vcf'] = 'text/vcard';
	return $existing_mimes;
}