You can call and message your friends, family and colleagues for free with Call.com by inviting them. You will receive a notification when your contact joins, and they will appear with a Call.com icon in your Contacts list. For free, you can talk to any Call.com contact. In the same time, you will be able to send them standard SMS and make calls. To do so, you will need to purchase some credits
To call non-Call.com users or send them messages, you will be charged and required to obtain credits.