Viber's core functionality is designed for communication between users of the Viber app. This means that to send messages through Viber, both the sender and the recipient need to have the Viber app installed on their devices. If you attempt to send a message to someone who does not have Viber, the message will not be delivered through the app. However, Viber does offer the option to call non-Viber users through its Viber Out service, which allows users to make calls to landlines and mobile phones for a fee. For sending messages to non-Viber users, one would need to use traditional SMS or another messaging app that both parties have access to. For any additional information or updates regarding features, it may be helpful to check the official Viber website or the app itself.