Reports are coming in of people being unable to get onto Singtel's 3G network this morning.
The fix is change the APN. You need to go to Settings / General / Network / Cellular Data Network. In APN, replace "e-ideas" with "Internet". Leave the username and password fields alone.
Thanks to @honcheng for this remedy. He learned this the hard way, via a dogged determination to get an answer from SingTel's Customer Service people. He fully deserves an award for perseverance.