Justin Timberlake, Muse, Phoenix and J. Cole will join Elton John and Katy Perry, among other A-list performers at this year's iHeartRadio music festival in Las Vegas. Clear Channel announced the performers Monday, which will also include Chris Brown, Bruno Mars, Maroon 5, Keith Urban, Miguel and fun. The two-day festival will be held Sept. 20-21 at MGM Grand Garden Arena, with host Ryan Seacrest.