Why are you trying to do this? In nearly all cases, you will get better quality and lower latency, usually with lower rates, by connecting to a VoIP provider directly, rather than using a "calling card" type of service.
In your example, both Google Voice and Callcentric have lower rates to India than Reliance and I would expect quality with either to be excellent. Did you have trouble?
If you have a heavy volume of international calls, you might consider adding a third service such as Voxbeam (good qualty at a decent rate) or Betamax (cheapest).