Start with why? see Simon Sinek Golden Circle about this.

Why do people need a directory app in this day and age? what inflection has happened in the market place for the time to be NOW? new technology, new culture, new laws?

What unique insight do you believe to be true about the market that others do not believe? What have you observed in the behaviours of your target audience that others have not capitalised upon?

Answer these questions convincingly, and show that a relevant sample of people care enough to spend $x - and that is your pitch