And lo, the music industry was revolutionised: Spotify has completed its iPhone app.

“We’ve finally completed work on the Spotify app for the iPhone and sent it over to the nice people at Apple,” says Spotify. “The application should be available in a few weeks for premium subscribers.”

As the video explains, the app has pretty much all of the Spotify features we we know and love. As hinted at previously, it features an offline playlist function, which syncs playlisted tracks to your iPhone allowing you to listen without being online.

It’s this offline mode that makes the Spotify app a potential iTunes killer. Why bother downloading a track if you can stream it and cache it on your phone? Despite the potential damage the app could do to iTunes downloads, Apple is likely to give it the thumbs-up, safe in the knowledge that the Spotify app will drive more users towards the iPhone. Of course, the Spotify app won’t be an iPhone exclusive – Android and S60 versions are unlikely to be far away.

For Spotify, the launch of the iPhone app will mean a huge boost in revenue. The app will be free, but users will need to upgrade to a premium Spotify account at £9.99 per month. The vast majority of Spotifiers are currently using ad-supported free accounts, but it always seemed unlikely that an ad-supported model alone could support the company. With millions of paying subscribers jumping aboard, Spotify’s future will look a whole lot more secure.

As for the artists and record companies, the (small) amount they are paid per play seems unlikely to rise, and the app seems certain to negatively affect download sales. Some artists won’t like it, and will try to pull their music from the service. But this is the future of music delivery, and those that don’t like it are going to have to lump it.

I originally wrote about the death of the download in January.

If you don’t already have one, here’s a post on the cheapest way to get an iPhone.

If you’re waiting for the Spotify app to appear for your Nokia or other brand of smartphone, here’s how to listen to Spotified music on your smartphone via Last.fm.

More Spotify stuff:
Five ways to make Spotify even better
Can Spotify save the album format?
Where is Beatles band on Spotify?

Paul Music, Technology