Mobile phones are a must in Hong Kong! There are numerous service providers in Hong Kong, all offering similar deals for new users.
Things to consider are:
How many minutes per month you think you are likely to use?
Will you be travelling to other countries?
Do you require additional services?
Voice mail
Call forwarding
Caller ID
International Roaming / China Roaming
International Direct Dialing (IDD) etc.
Most companies will provide a free phone, usually basic, inexpensive models, when you sign up with them. Or join the crowd by renting a mobile phone at the Hong Kong International Airport for short term use. If you own a mobile phone, you actually can buy a pre-paid SIM card from the service providers with a local number.
Registered Mobile Phone Network Service Provides:
PCCW Hotline: 852-100 0
SmartTone Mobile Communications Limited Hotline: 852 3128 2828
China Resources People Telephone Company Limited Hotline: 852 2945 8000