I've had the K550i for about a month now, and I think that it's the best phone I've had......having come from a long history of Nokia phones. All this talk about the screen being not as bright as others makes me think, is something 'wrong' with my phone? I've had mine next to a w810i and at 100% brightness, it's about 3 times brighter! I normally have it set at 70% to get a little more juice out of the battery...
I don't use it as a music device (I have a 8GB iPod nano for that), so the built in 75 MB is more than enough for photos/ringtones. This phone rocks for SMS storage, I have over 400 msgs in my inbox at the moment. Battery life is great (especially for talk times), reception is EXCELLENT (on par with Nokia 6230b, or better).
I've had no issues with the antenna being at the bottom of the handset... I haven't had one dropped call since I've had the phone...
The only thing i've bought is a Screen protector from Clarivue.com, keep the phone in a pocket with nothing else and you don't need a case.
Sony Ericsson K550i