For me, GO SMS Pro - Works like a dream!! I tried it out today while I was waiting in my Dr's office for 2 hrs  , and was reading and letting my family know how late I was etc. and their messages popped up on top of my book, I could reply to it without leaving my page, it was unobtrusive, and the best of all.... FREE!!
So I've found my solution... this one is the best for me.
Thanks for the help.

I checked out Handcent on Google play, and it said that none of my tablets are compatible with with the the program, only my HTC Desire HD phone. 
Any other suggestions that might work with tablets?

Sorry, I thought I made that clear... I have the Sim card, phone#, plan and unlimited messaging organized, the messages come through with simple messaging app, but I can only read messages, not reply or originate them. The messages show up top left notification, I can tap on it and read, but choice is only done, not reply or anything, and then it disappears.
The android phones have the full messaging app with the green square smiley face, and the tablets my provider sells have it installed too, but its missing with the nexus7.
I haven't had any luck finding the app on line.
Again, really appreciate any insight, and pointers.
Thanks