Spotify, which has become the talk of the town here in London, could launch in the US as early as September, reports the Observer newspaper. The music streaming service, which offers both ad-supported and subscription versions, is seen as not only a real iTunes contender but also compelling enough and the right side of “free” to wean users off of illegal file sharing networks.

I’m a big fan myself and am particularly excited about the up and coming Android, Symbian and iPhone mobile versions of the service.

See also: Music streaming service Spotify demos Android app, off-line syncing included!

Along with the incumbent iTunes — who offer a different model: ala carte downloads — Spotify will face much competition in the ad-supported and subscription streaming space. US-strongholds include services such as Pandora, iMeem, MySpace and Last.fm (ad-supported), along with Napster and Rhapsody (subscription).

One other competitor whom Spotify may or may not have had in mind when deciding to compete in the US is Microsoft (the underwhelming Zune aside). The Redmond giant is reportedly launching a similar service to European-based Spotify later this month.

As well as being an extremely well funded and resilient company, it’s thought that Microsoft’s service will leverage the company’s position in the living room by offering integration with XBox 360. We might also expect a tie in with Zune portable music players and/or Windows Mobile. Spotify on the other hand offers the slickest desktop client of all similar services (it’s incredibly iTunes-esque but without all the clutter) and, as already noted, its mobile plans are ambitious and progressing well. And this is where I think Spotify may have the edge.

Unlike Microsoft, it’s bound to be a lot more platform agnostic – any device, anywhere. That’s going to be the key to success for any ‘cloud’-based music offering.