I've been reviewing information on GSM in Singapore and note that they offer a automatic, free service called "Local Direct Dial" or "Local Direct Call" for calls to foreign roamers in Singapore. It looks like if a roamer is on a specific network, another user (roamer or local) on the same network can call him by dialing "#0"+CC+AC+NNNN. I'm not sure exactly how the call gets billed. Does the calling party pay just the cost of a local call or does the roaming party get charged for incoming calls?

Here are the LDD/LDC pages for StarHub & SingTel
StarHub LDC page
SingTel LDD page

Perhaps they realise they can subsidise the rate (below IDD, but probably above local calls) to call to a roaming phone because they'll also receive a part of the roaming fees back from the called phone's network

[I'm assuming]

Either that or they incur less cost by not having to send the call outside the country. Then it becomes interesting to know if they have kept the call secret from the roaming phone's network ....... I'd expect that pan-GSM agreements would be against this possibility though, so the first is more likely