Ok. So, it's like 1800 reverse, but for mobiles. You can call it from a pay phone, of from your mobile if you have no credit.
If you call 1800 mum dad, they'll ask for your name, so you say "*insert name here*"
then they'll ask for the number of the person you're trying to contact.
You dial the number, and it will patch you through to them.
When their phone starts ringing, they answer and it says
"Hi there, you have someone called *insert name here* who really needs to speak to you reverse charges. Will you accept the call?"
The person can accept the call, but it's quite expensive. If you're calling from a mobile you want to cheat the system, when they record your name, say "hi it's ___ call me back" really really quickly. When the person answers the call, they can hang up and call you back, and it's a standard mobile charge, not like $1.50 for 10 seconds.