When I'm on a date with one partner, I generally don't like to be distracted by texts or calls from another. Mind you, I don't have a primary partner who I live with, but with four partners, I can still get a lot of messages in a day if I don't communicate to them where I am and what I'm doing.
Usually I make sure my partners know when I'm out on a date so that they know to wait or send an email for later. Exceptions are made for emergencies, of course.
I don't mind too much if my partner gets a message or call from their other partners during our date, but again, if it gets to be a habit, is excessive (more than a text or two) or creates a distraction/spoils the mood then I'm not super happy about it and will tell my partner so.
One of the trickiest things about being poly can be focusing on the person you're with while you're with them. This includes things like not worrying about the kids, your job, what's on TV or what to have have for dinner tomorrow as well as thinking about your other partners. To me, when time is precious (as it so often is in poly relationships) it's simply respectful to make an effort to focus on your partner when they are with you. It is NOT disrespectful to send or receive a quick text message (unless you're actually having sex at the time.. that's a bit much).