If you don't want a member to be charged for the call because he already sent you a prepayment, you have two possibilities:

1. You can close (log out) the PayPerMinute plugin during your conversation. This way, the system won't count the duration of your call, and the member won't be charged per minute.

2. You can be the one who initiates the call, so the PayPerMinute plugin won't charge the member.