It depends on what I'm doing and where I am. I will usually wait until a time that is convenient for me. I don't like that mobile phones often come with the expectation that we are reachable all the time.
I only turn my phone on once a day when it is convienent for me, and then I might reply if and when I am ready. But, if that TXT is not with manners and a good effort of good English, it just gets deleted to where it belongs. Tough...yes, but my kids are learning....slowly.