Before leaving the airport, get 3G/4G prepaid SIM card (you can buy at money exchange shops) either from
Starhub or from
Singtel. Just tell them that you need only $8 SIM card and no other bundle.
The SIM cost SIN $8 and comes with $10 credit. Using that credit you can buy data traffic: Starhub
$5 for 1G data for 3 days or Singtel
1G data for 7 days.
So you will spend just SIN $8 and you will have your own sim card with data traffic enabled and won't depend on hotspot. Ask at shop to activate and check the data bundle and confirm that you can browse internet.
In terms where to have the call - better to hop on bus/taxi, come to Orchard st and have the call in a lobby of one of hotels.