You pay $19.99 a month, and get access to 95%+ of all recorded music in a lossless compression format. You can listen to this music on your PC, phone, ipod, whatever, but the deal is once every 30 days you must connect to the internet to re-authorize the content. Possibly for a fee, you could buy a longer authorization.
From a technological standpoint, I don't see how this could even work. You'd either need to invent a new format saddled with DRM and then somehow have every single type of music player adopt it (in order to meet the "re-authorize the content" part). Or you'd have a media format that could play on existing music players but then without the DRM defeating the whole re-authorization part. Which is basically what you these days with downloadable MP3s.