Some residential telephone lines have "duplex ringing" feature. Duplex ringing is to assign 2 different telephone numbers to a single telephone line. The ringing tones of the 2 numbers are different which allow the user to distinguish the nature of calls. Usually the primary number is associated with standard telephone ringing tone, while the secondary number is associated with fax call ringing tone.
As these two numbers are assigned to the same telephone line, you must register both numbers onto the Do-not-call Register if you do not wish to receive further unsolicited commercial messages at that telephone line. If only one number is registered onto the Do-not-call Register, messages may still be received at the same telephone line through another number which has not yet been registered. To find out if your telephone line is equipped with duplex ringing feature, you may check with your telecommunications service provider.
A lot of businesses usually deploy telephone equipments, such as keyline systems, private automatic branch exchange (PABX), etc, which can support call routing/forwarding features. Therefore, a fax sent to one number, may end up routed/forwarded to another number.
The telephone system administrator of your company should be able to provide information on the call routing/forwarding arrangements, in turn, allowing you to identify all associated numbers. You are recommended to register all associated numbers onto the Do-not-call Register if you wish to unsubscribe from unsolicited commercial messages. If your company or organisation plans to register 50 or more numbers on the Do-not-call Register, we can help you to register these numbers in one go. Please apply by downloading the relevant application form or through online registration.
Similarly, calls made to fixed line telephone numbers may be call forwarded to mobile numbers, or vice versa. You are recommended to register all associated numbers onto the Do-not-call Register if you wish to unsubscribe from unsolicited commercial messages.