There are a lot of positives about the 4GS that have been well covered, but for me, the overwhelming difference in the iPhone 4S compared to earlier models is the speed it operates at. Sure, the extra features are great (the camera in particular is a much better standard and the flash addition to the camera is more than welcome.) but for me, the problem with the 3GS was that it did occasionally feel a bit leggy with certain apps. That problem has all but been eliminated, and even apps that are quite indepth work quickly.

The phone isn't perfect - I find it much harder to drag ebooks onto my phone via itunes than I did before, which is frustrating as I now have to email them to myself and the Siri feature, which is a lot of fun, does have a little difficulty picking up my accent on certain words (I'm Scottish, so I'm used to this being an issue in voice command features yet I will forever be disappointed when I have to repeat a simple word 6 times to get it recognised) but these are small gripes.

The only real negative for me is the battery life. The battery in the 3GS wasn't great either, but I must confess that I was hoping for a significant improvement on battery life with the 4GS, but it's not as improved as I hoped. The increased capabilities of the phone perhaps account for that, but for the price, I would have loved a little more battery power.

Apart from those small issues though, I do think it is absolutely worth the upgrade.