Spotify has been working on a U.S. launch for almost two years, originally expecting to go live in this market in 2009. But some labels, most notably Warner Music Group, have gone on record stating their displeasure with the “freemium” model that Spotify champions, which offers unlimited streaming for free under an ad supported model designed to drive users to a premium paid service that eliminates ads and offers mobile access.

Spotify CEO Daniel Ek has insisted he wants to offer Spotify in the U.S. under a similar sort of model, with perhaps some changes to the length of time that the free version would be available.

Billboard’s sources say Spotify is open to short-term deals that would allow it to launch a framework of the service by the end of this year, designed to evolve over time as the in-dispute elements are revisited.

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Rhapsody remains ahead of the pack with the largest published subscriber base of close to 675,000 subscribers, although this number has been steadily declining.

Napster has continued to be a well-known brand name, despite being “the biggest loser” of the 2005 Super Bowl Ads.

MOG is fairly new service in the US (and soon UK) that offers unlimited streaming ($9.99/month) with a catalog of 8 million songs. Last week, MOG unveiled its long anticipated mobile app for the iPhone and Android.

Apple is a wild card. Shortly after Apple shut down recently purchased Lala, many speculated that Apple will step up with a global service of their own. Yet, the future of Apple’s place in online music streaming still remains unknown.

Same goes for Google, who recently hired music attorney Elizabeth Moody. They are rumored to launch a music service later this year along with the Android 3.0.