It is the business practice of sending all clients' billing info to a separate company, who then does everything for you. It also allows a company to cut down on time and human resources spent on administrative tasks.
There are several VoIP providers out there providing low international calling costs and rates. Ideally, you should choose a provider that covers the country you are most interested in. If you are located in North America and have family elsewhere in the world, then it’s in your best interests to find a provider that can offer great rates for the country you need. For businesses, you can sometimes get specific packages and negotiate with the provider for a great deal to cover your bulk calling to certain countries.