I thought it was a coverage problem at my place but looking at Twitter and other places, I can safely say that airtel EDGE went down in some parts of Delhi NCR region.
I am not sure if it is back now because my phone is currently connected to the web through Wi-Fi. But this is the second time in the last couple of months that I have noticed airtel network disappearing on me.
Mobile number portability is an option with me. Vodafone might be an option worth considering once I have spent 6 months on my current connection.