A method and an apparatus for providing mobility for a Voice over Internet Protocol Service (VoIP) provided on packet networks are disclosed. For example, the method receives a register request from a user endpoint device and retrieves an Access Point-address parameter from a contact header in the register request. The method then determines a physical location of an access point device in accordance with the Access Point-address parameter and updates location information for the user endpoint device in accordance with the physical location of the access point device.