Optus, Telstra and Vodafone now all offer a netbook with 3G wireless broadband access on a monthly payment plan (usually over 24 months with 1 to 5 MB of data a month). Optus offer the Samsung NC10, Telstra the Acer Aspire, and Vodafone the Dell Mini 9.
This is a very convenient way to get Internet access for email and casual web browsing. But you need to be careful not to exceed your monthly download limit on those plans where you are excess for excess data. It would be very easy to download a movie and end up with a large bill. Also the bundled deals usually cost more than buying the netbook and data access separately.
I use Virgin Mobile Broadband at $39 a month postpaid with my Kogan Agora Netbook Pro. This is not as convenient, as the Kogan does not have the 3G modem built in. I use an external HUAWEI E169 3G USB modem, which came free from Virgin. The Virgin plan reduces the data rate to 64 kbps when the 5 Mbyte monthly limit is reached, rather than imposing additional charges.