Okay, i know that not all of our phones have been as reliable as the STARTAC which you still see some people with because that thing is the tank of phones, but here is an example of a "bad" phone.
The samsung a650/670 had a known issue acknowledged by samsung regarding the hinge cracking and causing the phone to seperate at the flip. the problem was caused because the phone had a status light on the right side of the flip and that took away from the overall strength of the flip and created a weaker stress point. if the flip cracked it was always around the LED light and if seperated you could possibly lose your display (whether by blank screen or by the top half of your phone physically falling off). All later models such as the a630, a850, a950 , a930, a990 have learned this lesson as you can tell by much thicker hinges than their cousins, and also you will notice that not one of these phones has a status indicator light where the 650 and 670 had theirs