Streaming via 3G not possible?

I thought (but didn’t check) that one of the benefits of Match would be that I could stream my entire music collection to my iOS 6 iPhone any place any time anywhere so long as I had WiFi or 3G connectivity. It will stream or download by WiFi, and it will download via 3G (with the usual ‘charges may apply’ warning), but it won’t stream by 3G. Pick an album and unless I’ve previously downloaded it, the song-titles are ghosted out. Am I doing something wrong or does Match just not stream over 3G?