got an iphone From my girlfriend!

what you can do is restore the factory settings on the iphone.... my plugging it into the computer and itunes and it will ask you to restore from backup and you click NO.. (unless you want her apps on the phone) and then you need to call att and re-register it with you account as far as using the network goes

good luck!

Is the the 1st Gen iPhone? Restore as suggested, but you will need to obtain a new blank sim card from an AT&T store in order to activate it under you account (assuming you already have AT&T). The new sim card is free of charge.

After swapping out the sim and connecting it to your PC/iTunes, you will be walked through the activation process. The cost will be whatever plan you have now, plus $20.00 for "unlimited" data & 200 txt messages.

Ok, plug it into iTunes and sync with your new Mac it will remove all the old app's and music and the like. You can ignore a lot of the other information that other users have provided since you are in Australia, are you going to be using the same SIM card? or supplying your own or re-signing a new contract? if your going to be using the same sim then no problems just means the iPhone will be registered in your girlfriends name with the carrier just make sure you have yourself down as authorised to talk about the account. If you are supplying your own sim card or signing a new contract to use with the iPhone is it with the same carrier as the iPhone was with previously? if not you will need to get the iPhone unlocked and will need to contact the original carrier to have this done. Oh and don't worry about the first gen iPhone bit in the other comments it was never offered in Australia so unless you imported it from the US then got it jailbroken which i doubt as no carriers would support them (essentially meaning you would have a really expensive iPod) you would be fine on this count. Hope this helps

If you go with Optus as well you won't need to get it unlocked, Optus does do pre-paid you could just get one of those sim cards. If you went with a normal plan/cap and data pack though you would have to go on contract 12months being the shortest ones offered, which means if you take this option there's no backing out best to go pre-paid to begin with to reduce your copmmitments just watch the call rates and data rates though as pre-paid is always more expensive.