My theatre doesn't have wireless or other internet access in the rehearsal room or theatre, so we don't utilize IM. We're heavy Outlook users in the office. I would absolutely love, love, love to be able to IM questions to my boss or other co-workers during rehearsal. If I had the choice, I would use Google Talk.
I've been kind of late to arrive on the text messaging scene. Since I've got the cheapest phone service possible, I don't text very often at all since it costs me extra money. However, my ASM, being younger and much more cell phone savvy than me, texts all the time. It has never been a problem in rehearsal, I am glad to say. And, there have been occasions when I was across the building from her, needed to get a message to her in a way that didn't distract from the rehearsals we were both in, and text messaging was the perfect solution. I'm all for it.