I don't know many people using iPhone 4 any more as they are really outdated and most apps don't work properly with them any more. And most iPhone 5s have been phased out too. Still a fair amount of folks using the 6. I finally upgraded because the 6 stopped being useful for a lot of apps about 2 years ago. I tried to archive my chats when I upgraded and lost everything - oh well. Maybe it is all new and improved as we move forward. I still love using WhatsApp to communicate daily around the world.