I am seriously considering switching to T-Mobile, and I received a T-Mobile test-drive iPhone 5S today. I wanted to test WiFi calling, so I was thinking about installing iOS8 beta on it. I don't care about losing any data on the phone, so I'm assuming that it will be straight forward to revert to iOS7 before returning. Or am I missing something? Thanks, Ron p.s. I am a developer with a couple of apps in the app store.