The Friday night 9/21/22-Saturday morning 9/22/12 edition is in progress as I post this...like last year here in NYC, CHR Z100 (WHTZ) is carrying the show. There are likely approximately 150 stations carrying the show over the air; as previously mentioned, mostly CHRs.
Unlike last year, though, there is a hefty 80-90 second delay between the live internet video feed and the over-the-air radio feed in order to add profanity screening. I've already heard a few edits on the radio side.
iHeart Music Festival home page:
http://festival.iheart.com/go/iheartradio-music-festival/
iHeart online Listen Live page/link:
http://www.iheart.com/live/5158/?autoplay=true
Artist lineup with scheduled stage times for Fri. 9/21/12 and Sat. 9/22/12:
Friday, September 21st, 7:00 pm PT
7:30p PT / 10:30p ET: NO DOUBT
8:00p PT / 11:00p ET: MIRANDA LAMBERT
8:30p PT / 11:30p ET: MEGAN & LIZ
8:40p PT / 11:40p ET: BON JOVI
9:15p PT / 12:15a ET: JASON ALDEAN
9:45p PT / 12:45a ET: LIL WAYNE
10:20p PT / 1:20a ET: SWEDISH HOUSE MAFIA
10:35p PT / 1:35a ET: USHER
11:05p PT / 2:00a ET: GREEN DAY
11:50p PT / 2:45a ET: RIHANNA
Saturday, September 22nd, 7:00 pm PT
7:30p PT / 10:30p ET: P!NK
8:00p PT / 11:00p ET: BRAD PAISLEY
8:30p PT / 11:30p ET: CALVIN HARRIS
8:40p PT / 11:40p ET: NE-YO
8:50p PT / 11:50p ET: ENRIQUE IGELSIAS
9:20p PT / 12:20a ET: MARY J. BLIGE
9:50p PT / 12:50a ET: TAYLOR SWIFT
10:25p PT / 1:25a ET: LINKIN PARK
11:00p PT / 2:00a ET: DEADMAU5
11:15p PT / 2:15a ET: AEROSMITH
11:50p PT / 2:50a ET: PITBULL