Few years back, making a phone call to india from US was too costly (> $0.40 per minute), and there were few options. But lately there have been a complete change-over both in terms of price, and options. There are few main reasons for this - first, India's telecommunication infrastructre has improved tremendously with greater connectivity to other countries. Secondly, the economy downfall of 2001 was the start of ending of big US telecommounication companies. Thirdly, with the growth of Internet and especially with the arrival of voice over ip (VoIP) services, there have been a big price pressure.
I have always looked around for some comparision of different services, or a listing of possible options... but never found one. Here goes some basic things based on my experience