I don't think they've released it yet, but I don't think it's a big enough feature to warrant release early.
I mean, yes, we all want it (or most do), but it's nothing new. It won't make someone new buy the game, and most previous players will buy it regardless. So I don't think they'd release it till nearer launch, if they release it.
I would say its almost definite it will include a feature to migrate, but I seem to recall someone (can't remember if this was official) saying it was hard for them to transfer between DS and 3DS, so that may be a reason for them not to.