In Oz, the mobile carrier doesn't influence the cost of the call from a landline unless it is the same carrier as the landline (therefore cheaper).

charging for incoming and outgoing is a bit odd, I have free unlimited incoming and I pay 30c/minute up to $99 a month then I stop paying (up to $500) - that works out to be 1700 odd minutes and yes I do use that up cos I don't use a landline.

It's different as a landline to mobile caller because you know that the call will be expensive if you wish to talk for a long time - most of us just use a mobile to call a mobile and get our mates to use the same carrier for free calls to each other.

I think it's prolly easier that way out of courtesy, I don't have to explain to the caller that they should shut up cos I'm outta minutes...