This is one of the predictive dialer FAQ. The answer is copied here:
Predictive dialer is designed to help telemarketing agent to make outbound calls. It requires agents sit in front of the computers. In predictive dialing mode, the system will make a outbound call, if the call is answered by an answering machine, the system will automatically leave a message or skip to the next call; if it is answered by a live human, the system will pop up an alert window on an available agent’s computer. The agent can then pick up the phone and start talking.
An autodialer, on the other hand, is designed to have a computer to do all the work. The system automatically dials the next phone number on the call list, play a pre-recorded message after live pickup or answering machine prompt, collect touch tone feedbacks or speech command feedbacks. Once you start the voice broadcast, the system will take care of everything.
BroadcastByPhone also supports call transfer, i.e., the person who receives the call can press a key to talk to a live agent. The call can be transferred to a cell phone, for example.
From the customer’s point of view, when he answers the call, he will hear a pre-recorded audio message if call that is made by an autodialer; he will be connected to an available agent immediately if the call is made by a predictive dialer (he will not know that the call is dialed by a computer).
Based on the two very different usage mode, each program has different feature set targeted for that purpose.