The best way to make international calls

If the recipient has a smart phone with apps such as WhatsApp, Viber, using these apps is the easiest way to make international calls. They are free.

If the recipients do not have these apps and these apps are blocked (e.g., in China), there are a few other methods. Skype used to be the best way but it is discontinued. 

You can install an app on a smartphone to use it to call any number in the world.

mytello is supposed to be good, but the connection quality is quite poor.

Rebtel is similar to mytello but has much better quality. It is almost as good a using a landline phone. It just has a slight delay.