Today most of the people have a smartphone with instant messaging, audio/video call apps. When you want to make cheap calls to India from outside India the best way is to subscibe to an internet pack and use apps like WhatsApp, Messenger, Google Duo etc.
But what if the receiver at the other end doesn’t have internet. Here is where VoIP like Skype to Phone and Viber Out. The best feature in using VoIP is using the caller ID of your mobile no, the receiver will not even know that you are calling through skype. Anyhow to use this feature you need to have the mobile number verified and set it as the caller ID in settings. Note: To use Skype calling to phone nos in India the user should be in a country outside India and have an Internet connection to make the call.
Contrary to VoIP, there is another service which allows you to use the usual PSTN to make cheap international calls but through a local no that will connect to international number - and the best service provider is Rebtel. You can use the service for making unlimited calls after making a monthly subscription fee which is very nominal around 800INR.