Hi Yvonne can't help you with the question about Bathurst 1000 but can offer a bit of advice with phones.
Last year we took mobile phones with us and brought a sim card and put in in the phone. Then we texted home to let them know our number in case we needed to be contacted. You just have to make sure your phone is unlocked. We got ours unlocked in Bangkok but someone else will have to advise you where to get it done in Phuket.
Since there are 6 of you travelling together this way if you separate you can ring/text each other cheaply. It was also a lot cheaper to ring home than using international roaming....
I think that it is even cheaper to get a phone card and use pay phones but this is a bit inconvienient we found because of the time difference and you needed to go out to make a phone call and also find somewhere quiet where they would hear you.
Before we left Oz I went to Safeway ( or any major supermarket) and brought a $30 phone card designed for backpackers in Australia to phone overseas. You have to dial quite a few numbers but it is a lot cheaper for family/friends to ring you while you are away. Just go to a supermarket and see which company has the cheapest call rates to Thailand.
A word of warning if you are going to get International roaming activated on your mobile. It costs the person who rings you a lot of money and somehow they work it so that you pay for the call too. Also if the caller leaves a message you pay for the entire call and then to listen to it. Let alone all those people who ring that don't know you are overseas. There are better options available .
But of course remember no one can ring you until you send them your new number so do this as soon as possible and get someone to text you back so you know it is working.

Also don't forget oyur charger and remeber you will have to buy an adapter which are cheap.
Hope this helped

Enjoy your holiday

regards

Karin