Somebody found a prototype of Pokemon Ranger (for Gba not DS that's really interesting) which can interact with the Japanese versions of Pokemon Diamant and Pearl.
I follow the steps and I received not only a Manaphy egg but also the Azure Flute and I dump them here like that researches can be done.
According to him it can be the way to legit have the Azure Flute in Pokemon Diamant and Pearl and ask us to make it avaible for non Japanese version. So let's have some hard work ^^
-l