If you've got an iPhone, and you suddenly get a hankering to buy a song in the middle of nowhere, then you're fine - just head to the iTunes music store, put in your password, and you'll be listening in no time.
US Android owners have got the Amazon MP3 store, but BlackBerry users don't have anything to download songs from. So ringtone site Thumbplay has rolled out an application in the States for both Android and BlackBerry that lets you download tracks to your handset.
It's free, and available now for download on both platforms for US users. Check in the App Market for Android, and in the BlackBerry App World for RIM smartphones.