I am hooked on 3/4G and since my Nexus 7 3G, has it's own number... I have added it's own tablet 5-10$ plan to my phone plan. I use GO SMS Pro (it's FREE!) to send and receive texts to that number.
To make sure that I don't waste my data, I have the data turned off until I want to use it.
My provider (Telus) doesn't have the greatest tablet plans (in fact it's pretty lame!) but maybe they will introduce better. I've found out that the data sharing with your phone data, is not really useful for me.