just a suggestion, it's not a specific iPad app for texting, but can be used to make texting quicker since you say you do a fair amount of it, I just read about an iPad app today called TextExpander you might want to check out
Like everyone els I have had the same cell# for years and don't want to give out another # to get text on iPad but would be nice to get them pushed to the iPad.
After reading this post I like to try text free. But,
I cannot find text free apps . Hope some one can provide me the link.