I just went to make a phone call with the Motorola Q smartphone that I'm testing and, when I activated the sleeping display (by the way, there's no single button that does this without doing something else too.... something else you may not want to do), here's what I saw:
I'm not sure what exactly went wrong. I looked at the report details and, between a long list of dll files and lots of numbers (looked sort of like the hexadecimal dump part of a Windows Blue Screen of Death), they were not the sort of thing any mortal could figure out. I tried dialing the phone from another phone to see if incoming calls still worked and they did. But I also noticed that the email client that I use (from Good Technology) was dead.
Time for a reboot? Yes. Should you have to reboot your cell phone? No.