PHP で JSONP コールバックから JSON データを抽出するにはどうすればよいですか?

YAHOO.Finance.SymbolSuggest.ssCallback({"ResultSet":{"Query":"yahoo","Result":[{"symbol":"YHOO","name": "Yahoo! Inc.","exch": "NMS","type": "S","exchDisp":"NASDAQ","typeDisp":"Equity"},{"symbol":"YAHOY.PK","name": "YAHOO JAPAN CORP","exch": "PNK","type": "S","exchDisp":"Pink Sheets","typeDisp":"Equity"},{"symbol":"ETD","name": "Citigroup Inc. ELKS On Yahoo","exch": "PCX","type": "S","typeDisp":"Equity"},{"symbol":"YOJ.BE","name": "YAHOO JAPAN","exch": "BER","type": "S","exchDisp":"Berlin","typeDisp":"Equity"},{"symbol":"YHO.SG","name": "YAHOO","exch": "STU","type": "S","exchDisp":"Stuttgart","typeDisp":"Equity"},{"symbol":"YAHOF.PK","name": "YAHOO JAPAN CORP","exch": "PNK","type": "S","exchDisp":"Pink Sheets","typeDisp":"Equity"},{"symbol":"YHO.HM","name": "YAHOO","exch": "HAM","type": "S","exchDisp":"Hamburg","typeDisp":"Equity"},{"symbol":"YOJ.DE","name": "YAHOO JAPAN","exch": "GER","type": "S","exchDisp":"XETRA","typeDisp":"Equity"},{"symbol":"YHO.DU","name": "YAHOO","exch": "DUS","type": "S","exchDisp":"Dusseldorf Stock Exchange","typeDisp":"Equity"},{"symbol":"YHOO.BA","name": "YAHOO  INC.","exch": "BUE","type": "S","exchDisp":"Buenos Aires","typeDisp":"Equity"}]}})

<code class="php">function jsonp_decode($jsonp, $assoc = false) { // PHP 5.3 adds depth as third parameter to json_decode
    if($jsonp[0] !== '[' &amp;&amp; $jsonp[0] !== '{') { // we have JSONP
       $jsonp = substr($jsonp, strpos($jsonp, '('));
    }
    return json_decode(trim($jsonp,'();'), $assoc);
}</code>

<code class="php">$data = jsonp_decode($response);</code>

{
    "ResultSet": {
        "Query": "yahoo",
        "Result": [
            {
                "symbol": "YHOO",
                "name": "Yahoo! Inc.",
                "exch": "NMS",
                "type": "S",
                "exchDisp": "NASDAQ",
                "typeDisp": "Equity"
            },
            // ...
        ]
    }
}