The friendly staff at Changi Airport called around until someone came to open the Travelex booth. They quickly handed me my Singtel combined SIM & travel card. Took some time to get the SIM to work, as the number to use was on a label which sealed the card in a bag, and had to be split in half, through the serial number, to open. Tried to top up the travel part of the card, but the MRT station machines only accept Singapore credit cards, no cash. So I had to wait until the staff arrived at 6am. They only take cash, but I had some. With all that done the SIM and the transport works well.