Previously, any use of WiFi onboard Singapore Airlines flights was chargeable. But for as low as US$21.95, passengers can enjoy WiFi access for the entire flight.

However, things are going to get better for passengers travelling in Suites, First and Business Classes, as well as PPS Club members. As per the Singapore AirlinesĀ website:
Do take note that the complimentary WiFi allowances are not stackable (for a First Class passenger who may also be a PPS Club member). Also, the allowances are on a per sector basis. Hence, for flights with more than one sector, you’ll get to enjoy the same complimentary WiFi allowance for each sector.
I applaud Singapore Airlines for this move, given that WiFi access is increasingly becoming a commodity for all these days. Who knows, maybe the day will come when all passengers can enjoy free unlimited WiFi across all classes!