The software uses the Internet to send SMS messages, or if it's configured to be the default SMS application, it will consume SMS messages based on your plan which means that all the messages sent are displayed on your bill.
However, the company implemented Free SMS and the credits from the balance can be used to send a free SMS from a HIKE account. The messages won't appear on your bill because they're not related to the carrier's network. You still use the Internet to send them.