The easiest way to get a SIM card in Hong Kong is to buy one at a SevenEleven. These are not your father's SevenEleven. And they are everywhere.

You can buy them in several denominations, starting with HK$20. Calls turn out to be about US$0.03/minute. Dirt cheap. And by dialing what's called an IDD number before calling back to the United States, you can get the *same* US$0.03/minute rate for overseas calls to the States. The rate varies for other countries but is always extremely low. I was calling home all the time to impress the family.

There's no need to buy a higher denomination card because you can always add money to the SIM card at SevenEleven or directly with the carrier.