For the Tourist SIM Card, do I need to purchase it online or can I just walk-in at any SingTel shop in the airport to purchase it?
In the airport. Arrival Hall.
The money changers all sell SIM cards. Note there are several alternative companies supplying mobile connections, Starhub and Singtel are the main ones. There is no Singtel shop at the airport, they are around the city, but the only time we wanted one, there were long queues to buy anything.
It's best to buy it at the airport, because you need to show your passport to buy one.Edited: 13 October 2017, 17:19
Convenience stores like 7-11 and Cheers also sell the cards.