OK guys, thanks for all your inputs.

Based on your guidance, I have tested the following code with a
series of variations:

class foobar {
function bar2 () {
echo "Yep, in bar2() right now\n";
}

public function foo2 () {
$a = "bar2"; // Experiment 0
$a(); // Fatal error
}
}

And the variations:
$a = "bar2"; // Experiment 0
$a(); // Fatal error: Call to undefined function bar2()

$a = "foobar::bar2"; // Experiment 1
$a(); // Fatal error: Call to undefined function bar2()

$a = "bar2"; // Experiment 2
eval($a."();"); // Fatal error: Call to undefined function bar2()

$a = "foobar::bar2"; // Experiment 3
eval($a."();"); // Works but far from elegant

$a = "bar2"; // Experiment 4
$this->$a(); // Works fine

$a = "bar2"; // Experiment 5
self::$a(); // Works fine

So, I have a working solution right now. But I still don't understand the
essence of the differences between experiment #1 and #4. Also, I don't
understand the need to specify the class name in experiment #3, coming
from #2. Functions bar2() and foo2() are part of the same class foobar,
and I would assume that the name 'bar2' would be in scope of the function
foo2.

BTW: I'm running PHP v5.2.0-8 build and distributed by Debian (etch1).

Thanks again and regards, Paul.