Here is a Low Cost Calling App: Ringo- 19 paisa/ min STD Calls

Ringo lets you make low cost local and international calls without using the Internet (WiFi or 3G). You can call any mobile or landline phone number anywhere in the world. Now talk to your heart’s content without worrying about phone bills or internet connectivity.
Get the lowest local and international calling rates with Ringo. Our prices are 25% lower than most other calling apps.

For all calls with in India you need to pay 19 paisa/ min.

No Internet Connection Required.

Intro Offer: Get 50 mins Free STD Calls.

Calling rates for customers in the US

* Call Canada for 0.3 cents/min
* Call Mexico for 2.5 cents/min
* Call UK for 1.5 cents/min

Calling rates for customers in the UK

* Local calls within UK for 1 pence/min