The international code for Hong Kong is 852 and it is 86 for China.

For any enquiry regarding phone or telecom in general, see with the Office of the Telecommunications Authority:
Tel: 2961 6333
Web site: www.ofta.gov.hk/

You have different providers but here is the biggest:
Pacific Century Cyberworks Limited (PCCW Ltd)
39/F PCCW Tower, Taikoo Place, 979 King's Road, Quarry Bay, Hong Kong
Tel: 1000 or 2888 2888
24 hour sales hotline: 2888 0008
Website: www.pccw.com/eng/

All fixed line calls within Hong Kong are free. For all services to open an account, a Hong-Kong ID card or passport and proof of residence are necessary. Bills are sent monthly.

Here are some other providers you may want to check out:

• Hutchison Global Communications (HGC)
  9/F, Hutchison Telecom Tower, 99 Cheung Fai Road, Tsing Yi.
  New Territories, Hong Kong
  Tel: 2128 2828 or 2128 3388
  Website: www.hgc.com.hk
• New World Telecom
  17/F Chevalier Commercial Centre, 8 Wang Hoi Road, Kowloon Bay,
  Kowloon
  Tel: 2138 2138
  Website: www.newworldtel.com
• City Telecom Ltd
  Tel: 2926 1234
  Website: www.ctihk.com
• One Tel
  28/F Lancashire Centre, 361 Shau Kei Wan Road,
  Shau Kei Wan
  Tel: 2907 6000
  Website: www.onetel.com.hk
• EC Telecom
  Tel: 2157 2157
  Website: www.ectelecom.com