Few iPhone apps have been as eagerly awaited as Spotify for the iPhone. After months of speculation, development, and concern whether Apple would allow this iTunes rival on the iPhone, the app is available and sitting at the number one spot in the Apple App Store free downloads chart as we write.

Of course, calling it a free program is a bit misleading. Because - in case you haven't already heard - Spotify for iPhone is available only for Spotify Premium subscribers. Those are the people who pay Spotify £10 per month to use the service without the interruption of adverts.

So you can download the app for free, but the first thing it does is request your Spotify name and password. If you aren't already a Premium subscriber then you'll get an error message. Setting up as a Premium member is simple enough through the Spotify website and you can pay by credit card, debit card or PayPal.

Upgrading as a Premium member is instantaneous and enables you to use Spotify on your iPhone; it also enables Premium services on the Spotify desktop application.

Many of our US readers may have heard of Spotify, but won't have been able to use it yet, so here is our quick rundown. Feel free to skip to the bit marked 'What you get as a Premium member' if you already know all about Spotify.

What is Spotify?

Spotify is currently only available in the UK, Sweden, Norway, Finland, France, and Spain.

The service is a legal streaming music application for Mac and PC that works a little like iTunes, but with approximately 3.8 million tracks in the library. And they're not rubbish homemade tracks either - all the main record labels and a host of independents are backing Spotify. For example, the top 10 artists on Spotify are currently: Michael Jackson, Lady Gaga, Eminem, Beyoncé, Akon, Flo Rida, Kanye West, Kings of Leon, Green Day and the godawful Coldplay.

Thanks to deals with major independent labels, you'll also find plenty of smaller bands on the service. Having said that, there is a host of major bands that you won't find, including AC/DC, Led Zeppelin, Pink Floyd, Metallica and The Beatles.

You can create your own playlists: one particularly neat touch is that you can export and share playlists with your friends. And sites are springing up that compile playlists created by Spotify users.

But the main thing about Spotify - the thing that's garnered it so much attention - is that it's a free, ad-supported service. Users can legally download Spotify and instantly start searching and playing any of the tracks from the 3.8 million in the database; every four or five songs it throws an audio ad at you. The desktop app also has banner ads around it. It's not too obtrusive and certainly an acceptable way to listen to music.

But for £10 a month you can get rid of the ads by becoming a Premium subscriber. We've increasingly noticed local bars and cafes using Spotify hooked up to speakers - presumably paying the £10 rate.

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Digital World