In Reply to: If you take out the telstra sim and posted by gunn parker on Tuesday, 27. September 2011 at 20:52 Bali Time:
Save your phone contacts to your "phone" though first so you can still see your contacts once your normal SIM is removed and still be able to see them when your Bali SIM is fitted.
As freezn said, make sure your phone is unlocked though first.
To check this, see if you can borrow someone's else's SIM (pref someone who uses a different provider to you eg Optus etc), fit it to your phone and if it works then your phone is unlocked.
You may have to ring your provider if it doesn't to get them to unlock it, I have heard that they (Telstra) charge for this $27.50 if your phone is still under contract.
iPhones bought from Telstra can be unlocked for FREE see link below.
Good luck