If you install either one of the most recent firmware updates with an unlocked iPhone, doing so could very well render your iPhone useless.
If you perform a Restore, iTunes will use/install the most current firmware version available for the iPhone but I think there is a workaround to re-install your current firmware version instead.
This is a problem unlocked iPhone owners will be dealing with often or there is always the potential along with a voided warranty and no support from Apple. The benefit is using your carrier of choice but there is a significant tradeoff associated with doing so.
Did you purchase this iPhone already hacked or did you do the hack yourself?
If the former, contact the seller of the iPhone with hack for the unlock pre-applied and if the latter, contact the seller of the hack you used to unlock your iPhone for possible assistance.
All I can say is do it at your own risk. May want to review other sites that dedicate themselves to what you have done. It was VERY WELL made public news that the 1.1.1 update bricked many unlocked/hacked phones.