[cflee]

If you only have a 3G device, or a 4G device that doesn't support the available FDD-LTE bands, you might be better off getting a China Unicom HK card instead. They have HSPA+ on 2100 MHz. Google services work fine on them.

The cards are hard or impossible to find within the HKIA transit area, so you will want to either pick it from a street retailer in HK, or order from their English webstore - http://www.cugstore.com/hk_en/. Street prices are usually cheaper.

(No affiliation, just a happy customer from a few months back. I got their "Greater China 30 Days Data SIM" because I was spending time in Macau and Hong Kong as well.)