Misinformed by RedOne's customer service.. didn't give me the full picture.. just said prepaid SIM cannot switch to postpaid SIM that's all. Because of that I lost my old mobile number and had to change my phone number for many accounts including DBS Bank, Sing-Pass and Philippines embassy account for my helper.Prepaid to Postpaid only certain telcos. You can try Circles Life, SIMBA, Changi Mobile, M1 Maxx etc. most MVNOs of M1 support it.
Once converted to postpaid, you are free to port to other telcos. But make sure you check the T&C, some requires 1 month commitment etc.
Otherwise, convert from Prepaid to Postpaid in your incumbent MNO (ST/SH/M1) which is Starhub, then port out once converted to Postpaid.
This has been possible all along, you have been misinformed.

