In future we only need Two
Now there are too many computing devices in the market. There are smartphones, tablets, laptops and desktops…
As smaller mobile devices have more and more powerful processing powers, these devices will have a larger and larger overlap in terms of function, capabilities, and goal.
So, I see no reason why people want to keep so many things that do almost the same stuffs - more devices also means we need to bring more, or need to decide which one to bring. Other important issues are the device costs and carrier fees.
My guess is in the future we only need two (for each user) - a laptop (possibly a tablet-laptop hybrid) that mostly sits at home, and a phone/tablet hybrid device for on the go usage.