I recently logged onto iTunes and it informed me that a carrier update was available for my 3G iPhone. I originally purchased a phone in the US a year ago (with AT&T), and Unlocked it with redsn0w/Ultrasn0w when I moved to Australia. My new carrier here in Australia is Optus Turbocap Pre-Paid (WAAYYY better than AT&T). The unlock works fantastic and I am so appreciative of the Dev Team's hard work, but I am now curious about what to do when prompted for a carrier updates by itunes. I am assuming that iTunes is prompting a carrier update of my Optus SIM, but I want to make sure the update won't stuff up my Unlocked phone. Thank you for any help you can provide.

~eljefe27

It could break tethering if you have enabled it via a hacked method. Aside from that it's unlikely it will cause any problems and generally is a good thing.

Check here:
http://www.hackint0sh.org/forum/f127/78031.htm
and create a custom carrier bundle for your provider. It will allow tethering, MMS, data (if provided by your carrier) plus you wont get apples notes on updates that may break tethering aso