- Ease of use
I had bought a Sony DSC TX-10 but I rarely use it because it's more handy to just whip out my phone when that interesting shot presents itself. This is in spite of the fact that the Sony DSC is a portable series of cameras. It's just that my iPhone is more portable.
The mobile smartphone does more than just photos and videos. For that reason, you always have it on you when travelling. Digital cameras may not always be available unless you're going out on a prepared photo session. As an amateur photographer, you'd want to take photos of things like an impromptu group gathering or something interesting you saw on your way to work.
An interesting feature of smartphones is the apps. Apps provide primary-level image editing functionality. With just a few optional tweaks, I can make the colours in an image really pop or I can do something artsy. I can crop, rotate and apply some after-effects as well. An app on my smartphone can never replace Photoshop or LightRoom but there is something to be said for the ability to "spice" up my photos on the go. A great example of a professional photography app is Camera+ for the iPhone.
- Social features
Another thing that mobile phones have going for them is their ubiquity and a connection to the internet. Almost everyone has a smartphone nowadays and it makes sense that people would want to share these photos with the world. What smartphones allow is simple click-and-share or maybe click-tweak-and-share functionality. There's no lengthy process of copying images to your computer, editing them and then uploading the processed images to your favourite social network. Some services like Instagram have even gone a step further and tied their app to a social network exclusively for mobile photos.
In my humble opinion, smart phones are great if you want to take simple low-res pics on the fly. It would be very hard to take those really awesome shots that we see on shutterstock or in model portfolios with standard smartphones. For example; you'd have to be really pro to manage a bokeh with an iPhone 4S. That being said, future advances in technology may well prove me wrong.
(A couple of photos I took with my iPhone 4S)