Prepaid SIM card with free IDD service

There are plenty of prepaid mobile services in the market. In Hong Kong, all you need is just go to 7-11, and immediately you can get a SIM card and start to making call or receiving call. There is this card IDD Talk Stored Value SIM Card from Peoples, which I find that most suitable for tourists, expats, and other foreigners.

Why is that so? Because it provides Free IDD to 30 Countries/Destinations, including China. That means basically you can make a phone call to your home countries, and that is being charged for local call (about HKD 0.25 per min). The SIM card itself just costs HKD $60 with $58 value inside or buy a $98 with $98 value inside. Pretty a good deal.

So why pay roaming charge to call back your home while you are having fun in Hong Kong?