You need to sign in to an Apple account to get it going for the first time or to buy apps through the app store, or to do software updates. But you don't need to stay signed in or use the cloud services. Granted, it will pop up annoying notifications, but (at least so far) you're not required to use their servers. I have a second iPhone which I bought unlocked and don't have any phone service set up for. I bought it specifically to use as a camera. I can use it on my WiFi, not signed in, record video, AirDrop the files to a different machine, and never connect to iCloud. The day Apple starts doing what Microsoft is trying to do with Windows and remove the possibility of access without using the cloud will be the day I stop using iPhones.