Telephone number binding in a voice-over-Internet system is provided. One embodiment is a method for provisioning a customer voice-over-Internet device for voice-over-Internet service. One such method comprises: providing a customer voice-over-Internet device for communicating with an existing telephone line and a data network; providing a telephone number associated with the existing telephone line to a voice-over-Internet platform; and linking the existing telephone number to a unique identifier associated with the customer voice-over-Internet device.