Dingtone. Both available in Android and in IOS. Pretty similar to other free calling app out there. You can also use it as an walkie talkie Push to talk system which is different from many other apps we have seen previously also not available in many popular apps. It is full on walkie talkie. Also cheap rate to call abroad. For free trial they give you 15 credits which can be used to test performance. You can call India with that free credit for 15 Minutes and also any other countries depending on the rates.
For IOS Click Here
For Android Click Here
Enjoy.