Some premium rate services, for example for games and adult contents, are 11-digit.

In general, these numbers can be used across all carriers: The international call prefix varies depending on IDD provider, however 001 works on all phone lines and uses the IDD service provided by the same carrier as the telephone line that 001 call is dialed from.

Calls from Hong Kong to Macau and mainland China are international, and include that regions' country code: The present structure and format of telephone numbers in Hong Kong according to the Hong Kong Telecom Service Numbering Scheme, is as follows (the first digits of the telephone number are used as follows):[6] In the 1970s, area codes were assigned with the following pattern: There was no standard trunk prefix like '0' – only the area code and phone number were dialed when calling from one area code to another.

Area codes for seven-digit numbers were simply removed.

For example, in addition to the existing 3, 5 and 0 prefixes, a 4 prefix was used for Tuen Mun and Yuen Long, 6 for Tai Po and Sha Tin, and 8 for Hong Kong Island.