OR if you don't require Turn-by-Turn mapping, you can pre-load the Hong Kong map cache to the Maps application. Your iPhone must be unlocked and it's not hard to get everything done, use GMDL (
http://www.in7ane.com) to get the Google Map Cache and etc... Follow the steps from there.
I utilize this option as well as the use of xGPS on my iPhone 3G.
The searching for Address function may not work, but it's not hard to find the street name on the map and just walk on the street and find the right building etc..