Spotify's founder Daniel Ek has revealed more about the mobile version of the service, US expansion plans and a possible team-up.

At The Great Escape music conference in Brighton, Ek said the mobile app, that the company is working on for the iPhone, although with plans to launch for more handsets, would only be available to paid-up subscribers.

The current charge for subscription to the service - to get music ad-free, as well as access to premium content - is £9.99 a month, but can only be paid for by Visa or Mastercard, meaning some users who want to pay, can't.

"We want to be everywhere. We won't only do one device. Portability is an important aspect, [as is] interoperability with other devices", Ek said.

"That's definitely something we think is a premium product that people are willing to pay for - being able to bring the music with you or being able to have it working on your stereo".

The timescale for the launch of the mobile offering is said to be hoped for "before the end of this year", while the launch into the US market is said to be "at the end of the year, maybe the beginning of next year".

As far as the team-up goes: "We definitely want to have music recommendation", Ek said. "I'd love to work with someone like and I think in a couple of days you'll see some sort of announcement. Something will happen".

Despite Ek naming, other reports suggest Spotify is also looking at other companies for the discovery and recommendation features, with US-company Echo Nest tipped as a strong contender.

We will keep you posted.