Apple reveals the all-new redesigned, flat user interfaced iOS 6 today. The Apple has also released the beta for the developers to download and get their hands-on with the new iOS 7 and develop their applications. For running the iOS 7 your device should be registered to the Apples developers account. Below are the direct links and the developers account links both to download iOS 7 beta 1 for only the iPhone as said by Apple.
Download iOS 7 Beta 1 Direct Links (Un-Official)
iPhone 4 (GSM)
iPhone 4 (GSM Rev A)
iPhone 5 (A1428)
iPhone 5 (A1429)
iPod Touch 5
Download iOS 7 Beta 1 Developer Account Link (Official)