It seems a little odd for an as-yet unrevealed product to be the subject of an antitrust complaint, but that’s what appears to have happened in Europe.

Music streaming service Simfy says that it has submitted a complaint to Germany’s competition authority, The Bundeskartellamt, as it believes Apple is holding back the approval of its iPad app. Apple’s iCloud service, which it announced the official existence of in a press release last week, is widely believed to incorporate a music streaming element.

Simfy offers a Spotify-like on-demand streaming service, and is currently active in the German, Swiss and Austrian markets, with plans to expand further later in the year. “We believe there is a connection between Apple’s iCloud development and their blocking our application,” the company’s CEO Gerrit Schumann tells me. ”As we offer a true triple play streaming service (mobile, Web, desktop) – it seems Apple is worried about competition.”

“We have always considered Apple an important partner, but it is unacceptable for Apple to be able to control the market in this way,” continues Shumann, whose company already has an approved iPhone/iPod Touch app. “The App Store is a key marketplace we use to reach our customers. In the meanwhile,Simfy users are rightfully complaining about the lack of this app for the iPad. Of course, we ourselves are true fans of Apple and its products. That is why it was so disappointing and incomprehensible to us that we have apparently been blocked intentionally for months now.”

Ciaran O’Leary, or VC firm Earlybird which invested in Simfy in 2009, says that “We know (from an Apple App Store manager) that the app approval has escalated to the highest level within Apple (senior management approval council or similar) several weeks ago – still no response, not answering to letters from lawyers, etc – so it’s blatantly obvious they are misusing their power.”

Is Simfy’s complaint plausible? Could Apple hold back iPad apps from third parties to avoid competition with its own product? Given that music streaming apps from the likes of Spotify and Rdio (and indeed Simfy) are already available on the iPhone, it seems perhaps a little far-fetched that iPad apps with similar functionality would be held back.

That said, we don’t know for sure what Apple has planned for the music component of iCloud yet. Things should become a whole lot clearer in a few hours when the company unveils its cloud-based service in full at the WWDC event in San Francisco. At that point, Simfy’s action will either look like a wise move or just a shout for attention against a larger rival’s announcement.