Smartphones are everywhere. People use them in rich countries and poor countries. Sometimes very poor people have smartphones, even when they live in slums. I think that most people understand how important smartphones can be. For example, some taxi drivers would have less business without a smartphone. This is because they can find riders through an app and make more money than just looking for customers on the street.
Phones have changed a lot in the last 20 years. I remember when you could only make calls on cellphones. Now, you can take free classes from top universities. You can record a video, edit it and upload it to social media.
There are many apps available—over 2.8 million are available for download on the Google Play Store. Apple's App store has more than 1.8 million. Some people use these apps a lot. Research shows that 20% of millennials open an app more than 50 times per day. In general, most people use 10 apps each day.
Vocabulary
Slum [noun]; a very poor and crowded area, especially of a city.
Millennial [noun]; a person who is born between around 1981 and 1996, according to the Cambridge dictionary. According to Wikipedia, it's a person born between 1980 and the early 2000s.
Cellphones were invented in 1992, but the first iPhone was only released in 2007.