It doesn't happen with every network, I'm with 3 on a monthly cap and my phone charges are debited the following month after they were incurred.

It is very frustrating if they do not advise you that it is going to happen, although it is probably written in some terms and conditions in fine print somewhere if you look hard enough.
Yep - I came home and checked my contract and NO WHERE does is state that I will be charged in advance. I have been with carrier ever since I have had a contract phone and i have NEVER had this. I had 2 others check the contract and niether of them can see it written in the contract or terms and conditions either.
So know i'm certain I will be fighting it.
It may not see allot to some and to me i'd have to pay it anyway - but now it's the principal of it.