sg selling those call back card, it's lik a telephone card, juz tat u cn make overseas call. u dial the no, then hang up and aft which they will call bck n connect u to the no u wanted to call.
and such, the receiver no will show tat...
0301, 0302, private no, withheld, 0000
not to worry too much, even u ansa, no charges on u