How to use PDO to prepare and execute a SQL statement with the IN clause using an array?

Question

Possible Duplicate:
PHP PDO: Can I bind an array to an IN() condition?

I am trying to do the following:

$jsonarray = json_decode($incomingData, true);

$inString = '';
$delimiter = '';
foreach($jsonarray as $jObj) {
    $inString .= $delimiter.$jObj['number'];
    $delimiter = "', '";
}

$inString = "'".$inString."'";

$getFriendInfo = $dbh->prepare("SELECT user_id FROM users WHERE phone_number IN (?)");
$getFriendInfo->execute(array($inString)) or die("failure");

Basically, its a group of phone numbers in a JSON array being translated into comma separated form. Then, I want to insert the "inString" into the prepared statement. I tried the manual SQL statement and it works just fine, but using a prepared statement does not. Is there a different way to get that array of numbers into the prepared statement?