My Sprint Treo 650 developed this problem. I cannot unlock the key guard with the center button of the five way nav when in the phone app. However if I pop out then in my SD card it goes to the file manager and there I can hit the center button of the five way nav to unlock key guard and then everything works fine.
I have tried a warm and cold reset and the problem persists.
Any ideas before I head on down to my Sprint store?
Thanks!