Apple has released the first build of the iOS 7 Beta to developers



From MacRumors:

The first build, number 11A4372q, was released for the iPhone 5, 4S and 4, along with the fifth-generation iPod Touch and new betas for the Apple TV and a beta of Find My iPhone. Apple also released the first build of the Xcode 5 Developer Preview. Devices should be backed up using iTunes or through iCloud prior to installation of iOS 7, and following installation, can be restored through either process.

  Apple Releases iOS 7 Beta 1, Xcode 5 Preview to Developers