iPhone to Australia

[mezdef]

Hi, currently in America, and I'm considering buying an iPhone while I'm over here, cracking it and bringing it back to Australia to use with an optus sim. I'm wondering if it will work with the sim. I dont really want voicemail etc, just the normal functions like phone calls, sms, music. I've heard its comming out in Australia around march, but I wont wait unless I'm going to have real trouble cracking it, or if cracking it will turn it into a lump of plastic. I read around as much as I could but it all seems to be fairly vague, so a definitive answer would be nice. Thanks for any help.