Why should I choose a smart phone?

Because it costs more money.

And it's cool to spend money.

But seriously....
You classified this as "business phone" and you don't elaborate on how you use your phone. How do you expect an answer that will help you decide?

A smart phone is a great choice for business. It allows you to get email when out of the office. It keeps your calendar. It allows access to your work computer if you want. (I use vpn to access mine when I need to.) It allows you to take pictures and send them to others. (Job site photos can be sent to estimator.)

If you look at his posting history, it is a long trail of these one-line questions about phones and phone systems. He asks the questions and never returns to the topics, much like the folks who are always asking about converting pdf files to Word documents for editing.