I am going to have to give the exact opposite response to luffy.
Do not start texting while you are hanging out with people. If someone texts you and you do not text them back right away they should be mature enough to realize that you have other things to do in your life besides just texting.
I mean it is often a judgement call, if the text is really important obviously text them back or text them that you will get in touch with them as soon as you are free.
Consent texting while you are out with someone is the definition of rude. I took time out of my day to spend it with you, if you don't want to be here I could have stayed home and watched DVDs in my underwear.