I got the Sony Ericsson k800i about a month ago and have used it pretty much none stop.
My first thought when I unpacked the phone and turned it on was how hard it was to use the joystick. You end up pressing down intead of pressing it in, resulting in you selecting your language as Spanish (or something like that) by mistake. After using the phone for a few minutes though I got used to it. People who have tried to use it have also said that the joystick is hard to use, so it's not just me.
The first feature I tried was, of course, the 3 megapixelcamera the phone boasts. It is pretty impressive, especially as I was used to a VGA camera. The picture quality is good, taking big 2048x1536 photos. Unfortunately the camera seems to lose it's quality when taking "high quality video".
Texting is something I do a lot, and it's a bit tricky with the tiny buttons which are right at the bottom of the phone. This, like the joystick though, you also get used to.
As for what the phone looks like, well, it's pretty big. I personally think it looks alright, but the camera cover on the back sticks out quite a bit. I know it does this because it's supposed to double up as a desk-stand, but it's not really needed. On the subject of the camera cover, it's got no locking mechanism, so it tends to come open in my pocket, which enables the camera, so I sometimes get pictures of my pocket which isn't great.
The phone doesn't ship with a lot of memory really, so I quickly bought a 1gb memory card to store pictures/videos/music. The memory cards are tiny, and the memory card slot involves pulling a tab on the side of the phone pretty hard, which had me worried about breaking it. But it's pretty flexible.
The phone comes with some decent software which simplifies transfers from the phone to the computer and vice-versa. It took me a while to get it working (granted, because I didn't read the instructions properly - it turns out you *do* have to install drivers first). So yeah, that works now. But sometimes you have to plug it in a few times for the computer to recognise that the phone has been plugged in which is a bit weird.
Bluetooth is also a technology I use a lot, and I found that it works very well with other phones, except sometimes Samsungs (d500s and d600s in particular, although they are the only ones I've tested, apart from the d900 which works OK). I don't know exactly why this is though. Probably me.
Now for some final little things. There is an internet shortcut button on the front which loads up the internet when pressed. I have a bad habit of not putting keylock on when I put the phone in my pocket, and I can sometimes end up spending my credit on the internet when this button gets pressed. There is also a button on the side which plays music when pressed, even when the phone is on silent. This hasn't happened to me yet, but I can see myself pressing it by mistake in the middle of an exam or something. That wouldn't be good.
In conclusion, I would reccomend the phone to anyone. It has many more pros than cons, and it you're someone who likes to listen to music, take pictures and videos and browse the internet, this phone definately could be for you.
How helpful would this review be to a person making a buying decision? Rating guidelines
Sony Ericsson K800i - 3G - with Camera (3 Mega Pixel), MP3 Player, Bluetooth&FM Radio 2G more
Network GSM 900 / 1800 / 1900 3G Network UMTS 2100 Dimensions 105 x 47 x 22 mm Weight 115 g Display Type TFT, 256K colors Size 240 x 320 pixels, 2.0 inch, 30x40 mm Wallpapers&screensavers Polyphonic Ringtones(72 channels), MP3, Customisation Composer and Download Vibrate Alert Memory Phonebook of 1000 x 20 fields and Photo call Call records 30 received, dialed and missed calls Memory Stick Micro (M2) card slot 64 MB internal memory GPRS Class 10 (4+1/3+2 slots), 32 - 48 kbps HSCSD 3G ,384 kbps Bluetooth v2.0 with A2DP Infrared port USB, v2.0 Features Messaging SMS, MMS, Email, Instant Messaging WAP 2.0/xHTML browser, HTML(NetFront) Games + downloadable Camera 3.15 MP, 2048x1536 pixels, autofocus, video(QCIF), xenon flash; secondary video call VGA camera Java MIDP 2.0 RDS FM radio MP3/AAC/MPEG4 player T9 predictive text Image viewer Picture editor Picture blogging Organiser Built-in handsfree Voice memo/dial Standard battery, Li-Po 900 mAh (BST-33) Stand-by Up to 350 h Talk time Up to 7 h NOTE: English manual is downloadable from the Sony website as none is supplied