A method and apparatus for authenticating a communication device is disclosed. An system that incorporates teachings of the present disclosure may include, for example, an authentication system having a controller element that receives from a communication device over a packet-switched network a terminal ID and a request to authenticate said communication device, generates a first registration ID, stores the first registration ID and a first communication identifier, transmits the first registration ID to the communication device, receives from an interactive response system a second communication identifier and a second registration ID that the interactive response system received during a communication session with the communication device over a circuit-switched network, and authenticates the communication device in response to detecting a match between the first and second communication identifiers and the first and second registration IDs. Additional embodiments are disclosed.