OUT parameters for Stored Routines?

[eluser]nofearinc[/eluser]
I wonder how to retrieve the OUT parameters from the stored routines. It works OK with in parameters only, but I'm not able to retrieve the OUT values. My error is:

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Error Number: 1414

OUT or INOUT argument 3 for routine add_implicit is not a variable or NEW pseudo-variable in BEFORE trigger
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I use this approach:

Code:

$mail = '[email protected]';
$pass = '123123';
$out_id = 0;

$sql = "CALL add_implicit(?, ?, ?)";
$params = array($mail, $pass, &$out_id);

Any ideas how to bind the output parameters properly?