iOS beta 7 3 was released this evening by Apple and just like in the case of all beta versions of iOS, the American company set an expiration date. Unlike other versions of iOS 7Those from Apple Lossless Audio CODEC (ALAC), they chose to set an expiration date for this build of August 29, one month and three weeks from now, and after that date you will no longer be able to use your iDevices if you still have iOS beta 7 3 installed. Of course, in the meantime at least 2-3 versions of iOS 7 will be released, so you don't have to worry.
