On a recent trip to India, I had the pleasant surprise of finding a very nicely implemented free WiFi service at the New Delhi airport. The only requirement to access this free WiFi service is to have access to a mobile phone that can receive SMS messages. To access the free WiFi service one needs to get a username and password that is delivered via SMS in a few minutes after signing up.
Airports in general are boring places and getting a service such as WiFi without the need to supply a credit card is a welcome relief to anyone who distrusts using credit cards for temporary public services. I would also like to add that that unlike other airports such as the Dubai International airport, WiFi here was actually fast and usable and good enough for any kind of internet telephony.