<?php
$json = 'callback({"country_code":"RU","country_name":"COUNTRY","city":"CITY","postal":null,"latitude":0.0000,"longitude":0.0000,"IPv4":"00.000.00.00","state":" REGION\'"})';
preg_match('/^\w+\((.*)\)$/', $json, $match);
if (!$match) die('Malformed JSONP');
$data = json_decode($match[1], true);
if (!$data) die ('Malformed JSON');
var_dump($data);
preferences:
29.7 ms | 402 KiB | 5 Q