When I have carried phones and similar devices in hand luggage in the retail packaging because they are new, I have not had any problems. In all cases I avoided secondary screening by unpacking problematic things (bags of cables, laptop, ipad, etc) before screening and ensuring everything in my bag was in one layer of items so the scanner operator could easily see separate innocuous items. I have carried quite a few of these for friends and colleagues in countries that get new devices released later than where I live

The check of electronics that demands you turn them on is rarely applied and then usually only to US-bound flights. It has never happened to me. Additionally iPhones tend to ship partially charged, so if challenged by this I suggest opening the box carefully and turning it on for the security people, then put it away and explain to the recipient that security forced you to open it.