g only, Rated for 1 day of battery life.

support.google.com

9 pointsgrief2 comments

... and the most interesting bit is that some features (SMS and GPS) require an Android phone.

With weight, power, and space constraints, you're of course going to offload as much as possible to the phone.

You could probably do Hangouts without a phone though; anything that can be done over IP should be fine not needing the phone.