A predictive dialer does not wait for an agent to finish a call before dialling the next number. It watches how long calls last, how often people answer and how many agents are about to be free, then dials several numbers per agent ahead of time. When someone answers, the system connects them to whichever agent has just become available.
If the prediction is right, agents go from one conversation straight into the next. If it is wrong, two things happen: either an agent sits idle, or a person answers and there is no agent to take the call.
That second outcome is why predictive dialing is impossible on a personal SIM. A phone can only hold one SIM call at a time, so there is nothing to dial "ahead" with. Predictive dialing needs cloud lines, virtual numbers provisioned through a licensed telecom partner, where many calls can ring at once and be routed to whoever is free.