If you're streaming or downloading music or video over EDGE or 3G, you're violating your AT&T Terms. I wonder how YouTube works then?
Click this: http://www.wireless.att.com/learn/articles-resources/iphone-terms.jsp
The following is directly from the iPhone terms and conditions for AT&T:
"UNLIMITED PLANS CANNOT BE USED FOR UPLOADING, DOWNLOADING OR STREAMING OF VIDEO CONTENT (E.G. MOVIES, TV), MUSIC OR GAMES. FURTHERMORE, UNLIMITED PLANS (EXCEPT FOR DATACONNECT AND BLACKBERRY TETHERED) CANNOT BE USED FOR ANY APPLICATIONS THAT TETHER THE DEVICE (THROUGH USE OF, INCLUDING WITHOUT LIMITATION, CONNECTION KITS, OTHER PHONE/PDA-TO-COMPUTER ACCESSORIES, BLUETOOTH® OR ANY OTHER WIRELESS TECHNOLOGY) TO LAPTOPS, PCS, OR OTHER EQUIPMENT FOR ANY PURPOSE."
Click this: http://www.wireless.att.com/learn/articles-resources/iphone-terms.jsp
The following is directly from the iPhone terms and conditions for AT&T:
"UNLIMITED PLANS CANNOT BE USED FOR UPLOADING, DOWNLOADING OR STREAMING OF VIDEO CONTENT (E.G. MOVIES, TV), MUSIC OR GAMES. FURTHERMORE, UNLIMITED PLANS (EXCEPT FOR DATACONNECT AND BLACKBERRY TETHERED) CANNOT BE USED FOR ANY APPLICATIONS THAT TETHER THE DEVICE (THROUGH USE OF, INCLUDING WITHOUT LIMITATION, CONNECTION KITS, OTHER PHONE/PDA-TO-COMPUTER ACCESSORIES, BLUETOOTH® OR ANY OTHER WIRELESS TECHNOLOGY) TO LAPTOPS, PCS, OR OTHER EQUIPMENT FOR ANY PURPOSE."