It seems that Singapore telecom are following US telecom's fashion providing SIM only plan.
Singtel now provides SIM only plan which starts with $20 for 3GB local data + 2GB wifi data. You can customize your package by adding Talk time, and extra data, and SMS (who is still sending SMS?)
$5 for 200 mins, $10 for 800 mins, and $15 for unlimited mins.
$5 for each additional GB till 8GB, and $50 for 10GB, $100 for 20GB, and $150 for 30GB of data usage.