According to this, the American version of GTA IV will allow users to download MP3s from Amazon for use in the game.
Advertised throughout Liberty City, the cheekily-named "ZiT" technology is built into the game's mobile phone interface system. As players cruise around the world listening to the in-game radio, they can at any point 'mark' a song by opening their phone and dialing the number ZIT-555-0100. Gamers will then receive a text message with the song and artist names, and if they're registered at the forthcoming Rockstar Games Social Club community site, they'll find an e-mail waiting in their inbox with a direct link to a custom playlist on Amazon.com. All songs tagged "ZiT" will be stored here, available for preview and purchase at Amazon's going rate of $.89-$.99 per track. Best of all, those MP3s are free of the Digital Rights Management (DRM) limitations imposed on files downloaded through Apple's iTunes store and thus can be imported into any computer or digital device with no constraints.
We actually do want to play this now. Even though we live in the UK so wouldn't be able to download anything, and probably wouldn't even if we could. That's not the point.