Call completion is a telephony feature allowing some form of alternative interaction between parties who cannot converse directly with each other.There are several possible factors which can prevent a telephone call from connecting successfully: * Called party does not answer * Called party is busy in another call * Called party is off-line or unavailable * Called party actively disconnects the call before answering There are various definitions as to what exactly constitutes call completion.Generally speaking, call completion may encompass the following services: