Viber does the same thing and also has all the texting features etc... Not saying anything is wrong with your platform but, what's the reason for me to switch?

Viber does the same thing and also has all the texting features etc... Not saying anything is wrong with your platform but, what's the reason for me to switch? Can I send voice messages to those that aren't using your app? Or do I need have all my contacts download your application before I can use it to communicate with them.