How to get ios 5.1.1 on my iphone 3g?

When i plug my iphone into itunes it says its up to date but its not ios 5.1.1

I don't think you can update it to ios. I have a 3G too and tha software only goes so far.

You can try going to Settings>General>Software Update. I'm not sure if the iPhone 3G has 5.1.1, maybe the newer iphones and ipods have it. I'm on my iPod touch 4g and mine is 5.1.1

Your Phone Isn't Compatible

You need at least an IPhone 3Gs to run IOS 5.1.1 on your phone.