Welcome to the forum. Indeed, your 3g should be up to date. iOS is the Operating System which is inside your 3g phone, it should be call OS, but recentely the boss of apple said it's not called OS anymore but iOS just like the iPhone iPad iPod etc... There is a new release of iOS which is 4.3.3 instead of 3.3.3 but your 3g iPhone should not be able to handle that latest release iOS as it's very heavy and the hardware of your 3g will not be able to handle it very well. So like you have said up there, your phone is already up to date if you've reached the adviced last iOS upgrade for your device.
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