Summary from IRC:

This should be fixable by selectively populating arg_info in zend_std_get_method() with a structure that turns on the pass rest by ref flag.   That'll tell the macros in zend_vm_def.h to send the arguments by reference.  From there, you might need to modify zend_std_call_user_call() a little bit where it's building the args array... (Havn't looked close enough to be sure)

While addressing this, you should look at the return value as well, again this should be a minor matter of checking the __call implementation and flipping the return type in zend_std_get_method()...

<?php 
class Foo {
    function __call($method, $args) //NB 1
    {
        print $args[0]."\n";
        $args[0] = 5;
        print $args[0]."\n";
        return true;
    }
}

$v = 'str';

$o = new Foo();
$o->test(&$v); //NB 2 

var_dump($v);
?>

This code results in:
str
5
int(5)

So I believe this report can be closed.

You're forcing a call-time reference. How is this going to help when call-time reference stuff is deprecated?

I don't see how it is possible without forcing the reference OR having a method like __callByRef(), which makes little sense to me.

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Has this issue received any attention? I've noticed it cropping up elsewhere in the bug database. An example of where it is failing still:

    class TestClass{
        public static function __callStatic($function, $arguments){
            return call_user_func_array($function, $arguments);
        }
    }

    function testFunction(&$arg){
        $arg .= 'bar';
    }

    $test = 'foo';
    TestClass::testFunction($test);
    echo $test;

----

Expected result:
    string(6) "foobar"

----

Actual result:
    Warning: Parameter 1 to testFunction() expected to be a reference, value given in ...
    string(3) "foo"

----

By passing the argument by reference at call time, it succeeds:

    TestClass::testFunction(&$test);

Result:
    string(6) "foobar"

However, this of course begins issuing deprecation warnings in my IDE regarding the call-time passing-by-reference.

----

Any progress?