My personal preference would not be to ban any such devices - there are appropriate and inappropriate ways of using any technology. It is simply understanding the decorum, and acting accordingly (which I would phrase as respectfully). Those that don't use it appropriately, have a private discussion with them after lodge. Should the behavior continue, don't fear using the gavel. Playing Candy Crush during a degree? No - that's disrespectful not only to those engaged in the degree work, but especially to the candidate. Declaring that cell phones need to be off during degree work I have no issue with. As was suggested, if something that important is happening leave your phone with the Tyler.
Security risks? I agree that it's the man that creates that risk, and not the technology. I work on secret technology projects outside of the lodge, and wouldn't think of giving those secrets away any more than I would anything deemed secret in Freemasonry. That's simply being a man of your word.
Now, I do have one useful smartphone in lodge story. One Stated our secretary was on vacation and I was requested to take the minutes. I did it with my phone and a Bluetooth portable keyboard. Typed the minutes up in an email to the secretary, capturing them on-the-fly during the meeting. Worked great. I type at a pretty decent speed (as I've been pounding on a keyboard since the 70's), but being left handed don't chicken scratch all that well with a pen. If I had to do it on paper it would have been a disaster. If I'd had to drag along a computer to do the work I probably would have requested someone else do it. A 4 ounce Bluetooth keyboard in my apron case made this work - and my phone, being on silent, didn't ring once during the meeting.
Everything has its place - first and foremost, an understanding of the decorum required in any situation. Everything else descends from that understanding and the proper respect displayed for it.