Kyrylity messaging will not cost you extra. As long as you use your mobile smart device cellular data connection (4G/3G/2G/EDGE) or your mobile smart device is connected to a free Wi-Fi network.
Kyrylity uses your mobile smart device cellular data connection to send and receive messages to your contacts. You will not pay for every message as long as you have not exceeded your data limit. Messaging over a free Wi-Fi network will be free.
If your mobile smart device is roaming additional cellular data charges will most likely apply. It is therefore advisable to use free Wi-Fi networks (when available) to reduce your costs.