You can search internet for cheap rates and choose appropriate ones. By the way I use vonage, I get unlimited to many countries (Thought it is 5000 minutes per month good enough). Also I used to use Betamax (Freecall.com).
Check out:
www.phonecardsmile.com...ml?rf=2435
Before signing/buying any credit ensure that they provide SIP service. If they provide any kind of call in and connect, still you can automate it through sipsorcery.com. You can write dial plans such a way the calls connect through the service provider.
PAP2T-NA is a good one, but see that you get a original one. Lot of fake found in the market. If you see that the MAC id is pasted using a small slip, certainly it is fake. You can check online for a certain MAC if it is genuine from CISCO. I don't know the price of this device in India, but it should not be more than 1,500 Rs.
Let me know if you have more questions.