From your posts Wacko I don't think you are the type of guy to worry about saving a few HK$.
The local SIM's advantage to me is it:
* is temporary, you can ditch it if you get a stalker.
* is anonymous
* can be set to provide caller id
* calls made are invisible to work, or "she who must be obeyed". My wife may see my personal phone bill.
I use an old phone for this purpose so my normal phone stays up and running. I will never call home on the local pre-paid SIM phone, wifey will wonder why I am not using my roaming, or phone card. Likewise I use a pre-paid in OZ to call girls/establshments here, and to take messsages or talk with some honeys in Asia.