i have the w810i and as much as it frustrates me sometimes, it's a totally solid phone. i have a few friends who have the updated version that slides (can't remember the model number) and they have only had problems with it. some of their buttons don't work properly and things like that.
i've had the w810i for 2 1/2 years now, and after dropping it many times, it's still a champ. so i would suggest keeping it unless you upgrade to a smart phone like the blackberry or an iphone.