Yeah plenty of options in the states for cheap prepaid phone or SIM card - if you've got an old unlocked phone you'll save a few bucks taking and buying a just SIM card over buying a cheap phone.
Probably good to be aware that most of the prepaid plans in the states are blocked from making international calls... Im not saying that you'd want to be using it to call home regularly paying ridiculous $ for international mobile calls - but if you did need to call back for an emergency you won't be able to use it.
Another option is a TravelSim which works in every country and allows you to call anywhere - I've heard their call rates are pretty reasonable, but I think its a pay as you go system, so no extended call caps like most us phones will give you.
If you've go an iPhone or similar here, its always useful to take it with you even if you're planning to get a local phone and don't intend to use your Aussie phone for calls while you'reover there...
- you can keep all your booking details (flights, hire car, hotels etc.) in on place
- there's free wifi almost every in the states so you'll be able to lookup and book stuff online if needed, make calls or send messages back here for free using viber or Skype, and even keep up to date with everything on Seabreeze
or keep us up to date with your BOP results
- you'll have access to international phone calls via international roaming just in case you need to (I think some phone companies might require you to activate international roaming before leaving here but it shouldn't cost you anything to turn it on).
Just a few tips if you do take your Aussie phone:Make sure data roaming is switched off before you leave Australia (or it will cost a fortune just on incidental data usage your phone uses as soon as its switched on).
"International roaming" can be switched on to send & receive text or calls (remember this is different to "data roaming").
Turn wifi on so you can pick up local free wifi whenever you need to.
Don't expect to be able to use the GPS navigation on you phone to help you get places - as much as most smart phones have built in GPS capability, the navigation software usually uses data, so it won't work (unless you want to pay as much on you phone bill as you spent on flights and decide to turn data roaming on).
Receiving texts on your Aussie phone is usually free and it wont cost any extra for people sending them to you either.
Sending texts from your Aussie phone isn't too expensive when travelling (50c-$1) but often not included in a cap so it will make you monthly phone bill higher.
You will be charged to
receive calls as well as to make them, so...
I always try to remember to turn all voicemail services off before leaving the country - you don't want people leaving a message expecting you to call back, or to be continually getting texts from your voice mailbox telling you that you have a new voice message or that your mailbox is full (as you probably wont want to spend $ calling up to empty it).
Consider leaving a greeting saying you are away and won't be answering or returning any calls until your back (if its important they'll send you a text or email instead).
If your someone whose use to grabbing your phone and answering it soon as it makes a noise without thinking about it (can't say I've ever had that problem but I'm sure there's some phoneaholics that do), then I'd suggest leaving it on silent whole you're away - if you don't notice it's ringing you won't think about answering it, so it won't cost you a cent.
If you're really really worried about getting charged for others ringing you, I think you might be able to request you phone company blocks incoming calls while you're away (but I'm not completely sure about this) - or just leave the phone here and do without the benefits of having it while your away.
... And check with you phone company re. Charges for everything I've listed above because I'm sure they all have some differences too.
On another note (nothing to do with phones) if you're planning to hire a car and do a lot of driving while your there, a GPS can be really useful if you don't know where your going.... but have a think about how many days you'll be paying the $10-15USD surcharge to hire it with the car and you might find its cheaper to buy one here (if you don't already have one) and then buy the US maps online (about $100) and save them on your GPS before you go. That way you won't need to pay again and again to hire the GPS if you go back next year or the following.
PS have a great trip Andrew, you'll love the BOP!
Buying Sims in the Country your'e visiting is good and in some asian countrys such as South Korea is the only option you hire them at the airporA. Talk to your service provider they will usually give you good advice, or do Skype on your mobile. It depends on the country you visit. Even ring the RACQ on a motoring pretext and they give out advice, strange but usually true, get an international driving license at the same time they used to cost around $30.00 
