Decoding and looping through PHP JSON array

First of all the JSON you provided is invalid. Supposedly the valid one should look like this

 {
    "RequestHeader": {
        "mess": "am putting it on my wall....",
        "created_time": "2010-08-24T09:01:25+0000"
    },
    "context": {
        "type": "friends,circles"
    },
    "payload": [
        12345,
        12345,
        2345
    ]
 }

After you've fixed the problem with JSON provider it will be quite easy to access data

<?php

$json = <<<'JSON'
{
    "RequestHeader": {
        "mess": "am putting it on my wall....",
        "created_time": "2010-08-24T09:01:25+0000"
    },
    "context": {
        "type": "friends,circles"
    },
    "payload": [
        12345,
        12345,
        2345
    ]
}
JSON;

$data = json_decode($json, true);

$type = $data['context']['type'];
var_dump($type);
foreach($data['payload'] as $id) {
    var_dump($id);
}

Remember to make sure you check that the data actually exists before accessing it, e.g. isset($data['context']['type']) unless you are absolutely sure in it's integrity.

When you use json_decode method, the output will be nested arrays So for example to access context type you need to do the following

echo $decoded["context"]["type"];

And to loop on payload you need to do the following

for ($i=0;$i<$decoded["payload"].length;++$i)
{

$id=$decoded["payload"][$i];
//do some operation with the id

}