said by prestonlewis 
:Couple of things to consider:
1. Has India changed it's protective telecommunication laws? It was illegal to use VOIP since it cost the government owned phone company money. If things have not changed, you may want to use Yahoo voice, Skype on port 80, or Vbuzzer.com which also allows port 80 calls.
2. What kind of bandwidth do you have in India? Do you know which codec you need to use? If your bandwidth is limited, g729 (under 30kbps) is often OK to use. If your bandwidth is VERY limited, you might have to use the rarely used g723 low bandwidth codec which many VOIP providers do not support.
3. Lastly, does your India based ISP support SIP or does it block SIP ports?
You really need to know the answers to these issues before deciding how to use VOIP. Good luck.
Though not directly related to OP's question. I know a bit about your questions..
