Problem with iPhone software update?

I want to upgrade my iPhone to the latest software version but as I plug it to my laptop and iTunes opens up, it keeps telling me 4.2.1.is the latest version and my phone doesn't need an update.

Which version of iPhone do you have?

If you have iPhone 3G, then your firmware is up-to-date.

iOS version history
http://en.wikipedia.org/...on_history

Identifying iPhone models (How to tell which model you own)
http://support.apple.com/.../kb/HT3939

Edit: Reply

Then you have the latest version: meaning that you already have the newest version installed.

To make sure: See on Wikipedia 'where it says "operating sytem" right side: http://en.wikipedia.org/.../IPhone_3G

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