A month ago I had to call 911 for a medical emergency. At the ER I tried to notify my family of the situation. My Blackberry showed "911 emergency mode" and I was unable to dial out. Asked one of the EMTs about this, she just shrugged "I dunno". Punched up the phone mode menu and saw that I could turn it off. I imagine most smart phones handle it the same way.
Forgot to add the most important note. On the Blackberry the phone mode menu does not show the emergency mode options in normal use. It only appears after the 911 call is connected. Which is why I was unaware of it. Good idea to search phone mfr’s web/help site to uncover instructions.