It looks like ST is trying to sell out prepaid numbers that are expiring soon, by displaying them on the number board. All $38 microSIM, and there are so many of them (about 20). You can't get them in nanoSIM, and when I asked for nanoSIM numbers (not displayed) there were only 3 available. So few.
All the $38 nanoSIM numbers start with 8300. Activation expiry is about 1 year. It is only activated when you put the SIM card in the phone for the first time.
Free gift is travel adaptor. BTW SPass, EP, DP, etc won't be accepted. You need to have your passport if you don't have an NRIC.