Hi,
I am going to Australia for six weeks in the summer and I will be making lots of internal calls, so I am going to buy an australian sim card for the time I am there.

Is it possible to get a sim which I can use with the 3G network, and if so, is it free like it is here, or will I have to pay each time I use it?

Could somebody put a link up to a sim that would do the job, if there is one?

Thanks in advance, Tom.

p.s. My iphone is jailbroken and unlocked.

Yes we have 3G networks here, in fact all the networks in the cities are 3G. If you are staying in the cities all the time then go for 3mobile prepaid
Three - 3 Prepaid Caps

If you are travelling around the country (out of main cities) then you'll need Telstra (boo!) In my opinion, Telstra are crap, cost the most and have terrible cusotmer srevice. The only thing they have, is the largest 3G network coverage

Pre-Paid Mobile Phones - Telstra

hope this helps