That's what I use. I tried tablet talk but couldn't get Bluetooth working on my N7, and mysms uses wifi so as long as you have the wifi on both devices turned on it works great. Slight delay but not a problem!
I use Tablet Talk. I have the Nexus 7 and a Razr Maxx, also, and once you get the app set up on both devices it work flawlessly, updating in real time on both devices, no matter which you use to reply with. Bluetooth/wifi compatible, able to make and receive calls, It's well worth the money.
Tablet Talk. Best use of a few bucks that I've made in quite a while. I don't use my GNex at all now when I'm at home..which is a good thing: that phone needs every boost to its battery life that it can get