「Zend_Dateで」って言われるとこんな感じかな?

$s = new Zend_Date('2009-08-01');
$e = clone $s;
$e->add(1,Zend_Date::MONTH);
do {
echo $s->toString('d') . "\n";
$s->add(1,Zend_Date::DAY);
} while ($d->isEarlier($e));