Why can't i update my iphone 3g?

When i try to update my iphone 3g to itunes, it says "This version of the iphone software (4.2.1) is up to date"
every time i try to update it. It gives me a date, so i wait and when the day comes… It extends the date. So i don't know if this is a problem my phone is having or i have to keep waiting till my phone is ready to update.

4.2.1 is the newest version supported by your phone. If you want to run newer iOS versions, you have to get new hardware.

4.2.1 is the most recent version apple ios available for iphone 3g, as far as i know anything above this is for newer models so I think your fine, no need to update.

Thats the last firmware the iphone 3 can support.

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