I normally buy a US prepaid plan when I arrive in the US.
You need to make sure that your phone is unlocked. If you haven't unlocked your phone, ring Telstra and they will need to do it for you.
There are a number of options for purchasing a US phone plan. There are a number of Aussies that have bought plans/SIMs either online or from local places here to take it with them.
I tend to get to a phone retail shop when I arrive. My personal preference is AT&T because my family and friends are mostly all on AT&T. AT&T will give me the SIM for $0 when I walk into their shop and purchase a phone plan.
The plan I go with is the Go Phone Prepaid plan. I get the $2 per day prepaid plan which includes all talk and text. You can get one for the smart phones, if that's the type of phone you have. Depending on how long you are going for, they do offer a one month, $60 prepaid option that includes 2 gB of data.
Others on here will have their personal preferences. I would suggest that you stick with Verizon or AT&T for coverage purposes.