In this case, the fixed location plus the far field mic are great. When she's alone, she spends all of her time in her home. She lives in a pretty small place which means she can basically ask to start a phone call from anywhere and she'll be able to interact with the Echo. It's as much the hardware as it is the platform that makes it all work in this case.

I have no doubts the tech could facilitate something similar on Google and Apple's platforms but, afaik, building comparable functionality isn't currently possible (at least with Siri)—can you add arbitrary commands to either?

EDIT: the quickest interaction I could get away with was, "Alexa, start a phone call with {name}". No back and forth. One statement and the echo simply confirms (which was optional).