I've run this phone on a Vodafone contract for just over a year now. Previously, I'd had an SPV, which was great, but a little fiddly for many of the smartphone features. The K-JAM resolves every issue that I ever had with the SPV, and provides more functionality that I didn't know I wanted.
The first thing to grab your attention will be the slide-out keyboard. This is guaranteed to impress everyone when they see it, and it is as good as it looks. I find the keys very well proportioned, although I do have thin fingers - if you have bigger fingers, you might find it slightly more tricky. Although you have the option of entering data using the stylus (and the letter recognition software is impressive), the keyboard does make things so much easier. The only thing I dislike about the keyboard is the fact that some symbols are only accessible by tapping a button on-screen.
For anyone who hasn't used Windows Mobile 5, it really is a fully-fledged operating system, like you'll have on your PC. You can install a wide variety of programs, and the K-JAM comes with Word, Excel and Powerpoint pre-installed. These are not just document viewers either - they really do allow you to create and edit your own documents. Excel even allows you to turn your data into graphs, which is impressive on a little device like this.
This ability to install third party software also means that SatNav software, such as TomTom, can be put on there. I run TomTom on mine, and it works a treat. It even syncs with the addresses in your contact list, and allows you to navigate directly to any one of them. I've reviewed TomTom elsewhere, so wont dwell on it here.
The phone functionality does everything you could expect of it - voice dialling and so on are pretty standard these days.
The K-JAM has a 1.3MP camera, but this is helped along by software which interpolates the image to 2MP. The photo quality really is pretty good for a 1.3MP camera, but you wont buy this device because of the camera. The camera just isn't a reason NOT to buy it, is all!
There isn't a huge amount of memory and storage on this phone, and its conceivable that having a few of the programs mentioned open together could hold it up a bit. I've not encountered this problem, but if you do, there is an option to clear the memory of running programs - a bit like a RAM-freeing program in Windows XP. As for storage, the K-JAM takes mini-SD cards - mine has a 2GB card which stores more than enough music and pictures for my requirements.
Using Microsoft ActiveSync, you can synchronise with your laptop/PC. Contacts, emails, notes etc are all merged seamlessly, and you can decide what's synchronised. You can also explore and transfer documents via ActiveSync.
Its a shame that the K-JAM doesn't have 3G, and a slightly more powerful processor. With these additions, it really would be the perfect solution. The HTC TyTn has these, but doesn't look quite so good - it's probably a slightly better option than this though.