Unfortunately, this is a touchy subject for me.
I've been in countless projects over the last few years where the progress of the project and the personal interaction between the members have both been compromised by one (or more) of the members constantly fooling around with their phone during rehearsals, and sometimes even during gigs (grrrrr...).
IMO the personal and emotional interaction between all band members is critical to the successful performance of ensemble music - especially if improvisation is involved. Anything that disrupts this delicate interaction will compromise the performance of each individual member and the group as a whole.
And yes, I've also experienced the electronic interference generated by these devices that initiated this thread - not only is it annoying, but it adds insult to the injuries described above and is a symptom of a larger issue!
I've tried to be fair and understand both sides (emergency family situations, etc.) and I also acknowledge the benefits of being able to pull tab or a recording of a piece off the web in seconds to end what could be a potentially lengthy debate over what is actually being played.
But, unfortunately, my experience has been that the instances where the device is being abused (your definition of this may vary) have far outweighed the instances where it has been used to benefit the group.
Furthermore, I've attended performances by other musicians, most notably a recent Steely Dan performance in Phoenix, where I was appalled to look around me and see a large portion of the audience more focused on their phones (and obtaining their refreshments) than the show that they paid very handsomely to attend.
When did our perception of what is important and/or real shift from what is actually occurring in right front of us to what is being transmitted to us through a palm-sized electronic device - ?
Practice moderation in all things and don't be completely seduced by the lure of the electronic temptress (unless it has an Alembic logo on it!).
One last thing - I have two smart phones, one for work and one for personal use and they both know their place in the food chain = near the bottom.