I've been a fan of Sony Ericsson's phones for a number of years. I've stuck with them since I bought a Sony Z7 flip phone.
My last phone, a K700i lasted me nearly three years. It was dropped many times and showed it with plenty of dents and scratches, but it remained functional right to the end (the dodgy joystick finally stopped working altogether).
Anyway, back on topic. I bought a W880i recently, and have found it much more responsive in general than my previous one, except for one thing. It was really slow to unlock the keypad. I'd press the key combo to unlock it, and the phone would seem to freeze for several seconds before giving me control. This was getting annoying, so I decided to do a bit of debugging to work out why. After playing with the settings a bit, I finally tracked it down to the Orange Homescreen - a set of "quick" menus accessed down the side of the screen with the directional buttons. I changed it to the Sony Ericsson Homescreen (just a time and date with no menus down the side) and the delay was gone.
I've no idea if this problem is specific to Orange, but the phone supports (and presumably other models also support) an operator specific homescreen so it could happen to anyone. The delay was probably caused by the Orange Homescreen being overcomplicated (probably doing something stupid like parsing an XML file each time just to work out what to put in the menus).