I used to use Skype for calling clients, especially those outside the US & Canada. Then Microsoft acquired Skype and it became a disaster and has continued to be more and more problematic. So, I deleted my Skype account and got Wickr.
I did a lot of research before I got Wickr and it came out to have the best security and privacy. It's recommended not only for individuals but for military, government and corporations.
It is easy to use. However, strangely, they have no instructions on how to get it going. I discovered you have to have one contact first before the interface makes the phone icon available.
It's a clean, no-fuss interface. You can make phone calls, video calls and chat -- with anyone using Wickr. You can send files.
When you set up the account, you choose a Wickr ID or username. Other people can find you with your Wickr ID.
Most importantly, and the reason I chose Wickr, is because it's private and secure.