From my experience of reading posts on here I would be sending Drewbles a PM.
She already has i'm helping her out with some SIM cards
If inbound calls are important, the roaming SIM i'm providing offers a 1800 number for people here to call you at no cost to them. Outbound is a little moot though.
The AT&T SIM is $60/month unlimited calling and text, with 2 gig of high speed data (well, for AT&T it's called that but it's not overly fast in the USA). Text messages to AU numbers are included in this unlimited, but people replying will pay international SMS rates. Of course if you're sending a message to an iPhone, it'll use iMessage so that's just data allowance, and won't cost you or anyone replying in reality.
For voicemail, depending on your provider, setup a paging service. I use the Telstra service (Message Bank Memo) where someone answers (with a message i've defined) and the message is emailed to me. Optus, Voda and Telstra all offer this, although it can be tough to find people with a knowledge of it. Most have a subscription free offer, where you pay per message, or you can pay a monthly fee and it reduces the per-message cost down.
If you're dead-set on regular voicemail, the providers also can give you a number to call and login to. Speak to your provider to get the number. When you dial in, you enter your phone number, your voicemail PIN, and listen to it. You can then just dial out from the USA to an AU number to listen to your voicemails (perhaps after putting your AU SIM into your phone to await an SMS saying you have voicemail, so lower call costs).