Apple’s iOS ecosystem has never been as closed off to non-iTunes digital music stores as it may seem. It’s just a bit fiddlier to use rival download stores, whether using Amazon MP3′s desktop widget to import purchases into iTunes, or buying on 7digital then transferring those songs from its cloud locker to its iOS app.

Now Amazon has raised the game in its efforts to target iOS users by launching a mobile-web version of its MP3 store. The strategy is similar to 7digital’s: people will buy from the mobile website, then purchases will be synchronised to the Cloud Player iOS app, which caches them on the iOS device for playback.

“Since the launch of the Amazon Cloud Player app for iPhone and iPod touch, a top request from customers has been the ability to buy music from Amazon right from their devices,” says Amazon’s music VP Steve Boom in a statement. “For the first time ever, iOS users have a way do that.”

Amazon is an old hand at circumventing Apple’s walled garden due to its Kindle e-books store, which was built into its iOS Kindle e-reading app until Apple barred that feature.

As with Kindle, anyone wanting to buy music from Amazon on their iOS device can simply visit the company’s HTML5 store (located at www.amazon.com/mp3), pay for songs and then watch them appear in the Cloud Player app.

Understandably, the tech blogs are getting excited about this, with Business Insider taking the prize with its “Amazon Just Fired A Missile At Apple’s iTunes Business” headline.

Will that missile do much damage though? Even attracting a small chunk of Apple’s 500m iOS users away from iTunes could be significant for Amazon, although the short-term pain for Apple will be limited. The bigger picture, though, is of Amazon bolstering its position as a credible alternative to iTunes.