I'm not in Singapore, but I've been having the same problem since yesterday afternoon.
I just received an e-mail from my carrier (Indosat) that the problem affects 80% of BlackBerry users in Asia-Pacific, and that RIM is currently investigating this.
HTH
Posted from my CrackBerry at wapforums.crackberry.com
I get a higher rate of delivered message, but still, some of them either don't get through or take a long time to be delivered.
Questions regarding this problem are still commonplace in local user forums/mailing lists, so I think it's not fully fixed yet.