Anecdote: A user at work was assigned extension 112. Works fine on the Cisco handsets we mainly use, but when users were trying to dial it directly from their VoIP apps on their cell phones, they often got dumped out to the phone emergency menu (depending on which VoIP app they're using).

We're in NA so it was a huge mystery as to why this was happening just with their extension, took a while before we realized what was going on.