As was mentioned above, they've had this for a few years.

You need to use their app to scan your passport and your face - and you can only do that once you are physically in Singapore. You can purchase the eSIM and install the app before arriving in country, but you can not go through the registration process beforehand.

As at last time I used it, the self-registration process does NOT get you sms/voice, only data - even though the plans do include voice. I've been told you can go to a Singtel store with your passport to activate voice but haven't tried, however it would make sense given that SIMs purchased at SingTel stores (with a passport) do support voice/sms.