From what i read z1 and zym cso are not giving the promotional new sign ups and port in offer currently that is tied with 365 days limits. vivifi i left long ago not quite sure...
Those appear to be tied to churn requirements, based on how they worded it. I am guessing Singtel must have directed them to offer it only to new-to-Singtel customers, so either new line or port-in from non-ST.
I think customers might still be able to ask for the 500 IDD minutes and the 20GB roaming since those don't look like they have churn requirements.
Operators also measure churn - "how many customers jumped from their operator to mine" - as part of their benchmarks. The implied assumption here is that "customers left their previous network cos mine is better", so they use this metric for investors and marketing. That's why these carrots are dangled to generate churn.
Singtel is very blatant about this - so they tie all new customers to 12mo contracts (except for some exceptions in the past year) to stop churning out. Even seniors, where it makes no sense. I worry that other operators may employ this strategy soon, so it limits our choices. It's worth noting that SH has control on its sole MVNO - Eight.