I am not the biggest fan of mobile gaming, but I found one that I really like recently.
Basically, you have to balance a grid by connecting cities and power plants, using the logic and basic principles of an electrical grid (overload, fault protection..).
The first levels are fairly easy, but from level 16 is quite challenging to reach 3 stars.
The best part, in my opinion, is that the game has been developed by the Norwegian network operator!
It's called Balanses (no, it's not bad English but Norwegian )
Android link, not sure if there is an iPhone version.