There are two types of Reverse Charge Call(well in the UK at least).
1.Through a BT Operator,who asks the called person if they will accept the charge,and if they agree bills them and not the caller.
the above calls are expensive due to going through an operator,
so nowadays a the Automatic Reverse Call is used.
2.Simply,the person calling (who wants the other person to pay for the call) dials a special number followed by the number of the person they are calling.
The person being called gets a message which in effect says"This is a reverse charge call, if you are willing to pay for it please press(whatever key) now"
They are then connected,and the equipment then charges the person being called,plus a charge for the reverse charge facility.
However,please bear in mind that if you are calling from a Payphone or a Mobile,the person being called WILL be charged at the Payphone or Mobile rate,not at their home phone rate.This can mean some of these calls can work out very expensive.
I hope this is clear.