Internet usage converted to MBs and GBs?

Does anyone know how many MBs or GBs you use by surfing the net in a month – including things like Google searches, loading news pages etc… the occasional flash site or whatever, maybe if you are online 4 hours a day? And also how many MBs or GBs of data an hour long conversation (no video) over Google Voice is? In Australia you buy internet access by the MB so I’m wondering how much I use typically…
If you are ever in Oz or NZ, just know their internet infrastructure leaves A LOT to be desired. A LOT.