Sorry, I'm late to the thread, but Samsung makes close to what the OP wants.
The Gear S:http://www.samsung.c...oducts?filter=gear-s
Has its own SIM card so it doesn't need to have a phone nearby. You can make/receive calls and text messages. It's basically another stand-alone device on your wireless plan. Battery life is supposedly 1-2 days.
Helpful tip: Probably best if you're sitting down when you price it out.