goodness, what a thought ><. Not too far back we called 911 on a cell phone that we didn't know had the microphone shorted when it had gotten wet earlier in the day but otherwise was completely operational. Took several minutes to figure out what was going on. I think we wound up texting a friend that we'd call them and to verify they could hear us or not. We wound up having a headset handy luckily enough.
No. It was a basically stock Verizon edition of Android.
After that experience I switched to iPhone. However, since then, I've experienced the iPhone iCloud Phone.app crash, which also denied me 911 service (although fortunately I noticed the problem and resolved it before needing 911.)
I've actually had this happen in an emergency. I can't tell you how dismayed I was that my phone crashed when I called 911.