These are blocked by default, but this code snippet should do the trick when added to your functions.php file:

function simpatico_upload_mimes_vcard_support($mimes = array()){
    $mimes['vcf'] = 'text/vcard';
    $mimes['vcard'] = 'text/vcard';
    return $mimes;
}
add_filter('upload_mimes', 'simpatico_upload_mimes_vcard_support');