I've been using my C550 for a few days now, and to be frank I'm sorely disappointed with the user experience Windows Mobile provides. Things that should be simple aren't, things you should be able to do you can't and things you expect to be able to find out require you to download additional software.

For instance, when writing a text, if you for instance mistype a word, or forget to select the correct word from the T9 list, you can't then go back to that word and see what other permutations were valid in the T9 dictionary to correct it; you have to delete the entire word and start again. You seemingly can't change the earpiece volume mid-call, something that's hugely beneficial if you're in a pub or crowded room and want a volume boost. You can't seemingly navigate around your phone mid-call, you can't silence your phone but let it keep ringing (for instance if it's at night and your phone goes off, and you want to move to another room to answer it to avoid waking up your flatmates...), there's no immediate warning that you've gone over the 160 character limit of an SMS...

They're all little points, but they build up into a fairly unpolished OS for a phone. Other companies have had been at this for a while, so it's to be expected that their user experience will be more polished, but there is no shortage of inspiration for how to design a good phone UI. From a technical standpoint, the phone falls down too. The screen is very difficult to read in daylight conditions, it has an astonishingly poor 2 minute boot-up time from off, the battery life is sub-par, the camera is useless in low-light (and there's no flash or LED to help brighten things up), the camera's response time is shocking (nearly a second from when you press 'take photo' to the image actually being pulled from the CCD), the video resolution and framerate are dismal...

In short, don't get this phone. Ever. Get a SonyEricsson k750i or similar, it's a nippier, sleeker, more user-friendly device and it doesn't make me rue the day that I signed a 12 month contract to get this pile of crap.