SingTel Tag Lite
SingTel mentions 'Tag Lite' nowhere on its website, so the only way to learn about it is to visit a SingTel Hello store. I first heard of it on a Hardware Zone forum thread about using MultiSIM on the iPad.
MultiSIM
SingTel MultiSIM, one number across several SIMs.
SingTel Now Supports MultiSIM For MicroSIM
Finally, SingTel supports MicroSIM cards in its MultiSIM plans, though at twice the price of normal SIMs. Only one MicroSIM is allowed in any combination, so with four SIMs just one can be MicroSIM and the rest normal.