Since iTunes Match went live, I enabled my account and uploaded all of my music (over 16,000 songs). When you enable iTunes Match, it deletes all the music on your iPhone and forces you to re-download all of it through the Music app. After 5 days of re-downloading all of my music, I was receiving numerous warnings from AT&T indicating my data usage was close to exceeding my 4GB maximum, and then I did exceed my 4GB. 15 days into my billing cycle, I was at 5GB whereas my average monthly use is 2GB or less. I looked into it, and my data usage went from a daily average of 50MB/day to, after 11/14 when I enabled iTunes Match, 200-300MB/day. After 90 minutes on tech support, we found the culprit: Settings -> Store -> "Use Cellular Data" Prior to enabling iTunes Match, the toggle's text beneath it simply indicates turning it on will use the cellular network automatically downloading purchases (purchase something on your computer's iTunes, and if your phone is on 3G somewhere, it automatically downloads the song/app if under 20MB). Well, after enabling iTunes Match, the toggle's text becomes: "Use cellular network for iTunes Match and to automatically download purchases." If you queue up as much music as you think to carry while on wifi, but then leave wifi, the phone will continue to try and download it once on 3G. If you carry 10+GB of music, you can see how quickly this may go over your monthly allowance (as I already have). So far, there isn't a "pause all downloads" button in the Music app that would allow you to hold the downloads and resume once on wifi, so unless you know to toggle this on/off, your iTunes Match downloads will continue unless you turn off all cellular data (thereby cutting off email, web browsing, etc). I would imagine, if you're on 3G and want to download new albums, you'll have to disable this toggle, download the new stuff, then re-enable. I asked the Apple support supervisor to possible bubble the idea up to a supervisor to include a "pause all iTunes Match downloads" within the Music App, or something more clever. Just be wary of your data usage with the iTunes Match, and if you're downloading a lot of music, make sure you're setting this toggle appropriately.