Mantra online is not the cheapest ISP around nor the best (I still prefer VSNL). However since it has its own gateway and doesn’t use VSNL’s like the others, you will often find it possible to access it when all others fail. However it is pretty slow and you get disconnected quite a few times. All said and done, one should use it primarily because of the reason that it provides a good backup service when ones main ISP is down.