Nymgo is a recent addition to cheap calls to India. It is provided by Splendor Telecom UK. As the other voip providers have, nymgo also has a client to make calls over the internet. They have two kinds of plans, charge per min and flat rate monthly (of course theres a limit you can talk). The scheme which attacted me was the monthly plans. For example the asia and australia plan costs $20, which comes to approx 15euros. This plan gives you monthly talk time of 1750 minutes, hence the cost per min comes up to 0.008 euro cents, even less than 1 cent. This is the cheapest viop provider I have come across till now in comparison to Freecall.com (2 cents/min), justvoip and others.
Their pay as you go scheme is also quite comptetive compared to other schemes. The voice quality is superb. I havent had any problems with the voice quality. Although when I signed up there were acute problems with call setup, but the support team are very prompt in their reply and fix issues quite fast. I would say its a rather reliable voip provider.