A teenager usually starts out with a cheap model of a car, a bike or a cell phone. They are excited about their first phones and will not mind even a cheap one as long as they have one. This helps them to stay in touch with their friends 24/7 and is a way for parents to communicate with their kids while they are out. Most parents get their kids a cheap phone so that communication becomes a lot easier. Even if they can afford a fancy and expensive cell it is best to start with a cheap one so that the teen gets used to taking care of his property and becoming more responsible.
A cheap cell phone is not because the teenager does not deserve an expensive one, but it is because there are more chances of their loosing their cells in the beginning until they get used to owning one. If they own an expensive cell it would be a lot more difficult for them to replace it and this is why a cheap one is always best as a first mobile.