the idea is having a LAN with an Asterisk server installed such that if someone connects to the network, the asterisk server gets to know about the 'joined client event' connection and consequently creates credentials necessary for that client to place a voip call to another person on the network. am new to both voip and asterisk, so please bear with me for i dont know if even such a function is in existance. thanks
You need read about asterisk realtime architecture.
But anyway u need write voip client to support auto-config.