From GSM Arena:
The Nokia 5800 XpressMusic was a good phone for its time and with 8 million units sold in the first year of availability, it proved to be a commercial success by the Finnish giant, which was on top of the world. But if we remove our rose-colored glasses, we can see that this phone marked the beginning of the end of Nokia’s dominance.
When it came out in late 2008, the 5800 had just about everything you can want from a smartphone. It was a hybrid between the capable N-series and the media-driven XpressMusic, it came with a rich retail package and an attractive price tag.
To their credit, the Finns released several major updates to the OS that significantly improved the performance of the phone and the usability of the interface. Still, they were trying to drag a 20th century OS into the 21st and it wasn’t going to go easy...
...Comparing the Nokia 5800 and the contemporary iPhone 3G, the Symbian phone has clear advantages. Its screen was sharper and with a media-friendly 16:9 aspect ratio, the camera was higher quality and it could shoot 480p video (which wouldn’t be available on iPhones until a year later with the 3GS). It had stereo speakers and expandable storage too.
But the iPhone had a responsive, finger-friendly capacitive touchscreen and a UI that was designed around it, including multi-touch gestures. The Nokia came with a resistive touchscreen and a stylus that slid into the phone (plus an external plectrum). Worse still, it lacked basics like kinetic scrolling in menus and predictive input for the on-screen QWERTY.
Go read the full article, it's quite long but worth a read. All written with hindsight, of course, but pretty accurate in summary.
And yes, so many 'what ifs' surround this period of Symbian's history - have a read through our article archive from 2008-2010 on this site for much, much more.
The N95 8GB (on the left), the 5800 XpressMusic (centre) and the N78 (on the right)