A nicely unpolished video from Digicel Papua New Guinea on what connecting the next billion actually means.
In no particular order:
People steal the solar panels (this is an even bigger problem with diesel generators)
The network goes down if it rains for too long
Access to power of any kind is crucial for your users
How many different distribution networks does a mobile operator have to build?
Most of those sites probably aren't going to be able to handle everyone in the area watching YouTube (hence - data pricing, zero-rating and the problem with net neutrality)
In the next 5-10 years, almost every single person you see on the screen is going to own a smartphone. What they pay for data, and how they think about charging, is another matter. Meanwhile, one might suggest that for some of them a mobile phone is the first electrical device of any kind they've owned.