There are things that you can do as soon as you get a second iPhone/iPad.
1 – You can use one to find the other if they are both yours. Where
did I leave it…?
2 – You can find your friends. If the second one is for someone else,
now you can see where they are there or on the way home etc.
3 – You can share pictures with each other. We do this one in my
family very often. We have shared Photostreams full of babies. They
download passively and are just there on your phone
4 – You can collaboratively post to those photos. Anyone who has
access to the photostream also can post if you let them. This is
different from most other sharing sites on the Internet. It is also
better. Because the babies getting passed around are photographed by
all parties.
5 – You can FaceTime each other. I don’t do this very much but hear a
lot of people do.
6 – iMessage. Whatsapp for iPhone. I use this often without thinking about it.
7 – You can backup from one device to another. You can download apps
to multiple devices. This is boring. Android does this ‘natively’ too.
8 – Gamecenter. Nobody cares about this one though.
9 – AirDrop to send files to each other. I never do this though.
10 – I suppose you get some benefits from AppleTV and Mac ecosystem
like this too — e.g., using the screens via Airplay or using as
alternative input device.
Many of these things are app-driven add-ons in Android but they aren’t
native and I think it shows Android is less of an ecosystem. It’s
really the place Apple is seeking to beat back the wild and woolly
Android world.