I had never thought about how the rules prohibiting cameras in many courtrooms would apply to smart phones. I'd call the Bailiff (or the contact number listed on your summons to jury duty) and ask.
I'd guess there is a fair chance you'll spend some time waiting to be called....Possibly inside a building with poor 3G (we won't even talk about 4G) reception (and that sucks the battery anyway). I'd have some good time killers loaded that don't require web access or sound. An ebook reader and a book or two that appeal to you would be a good option if you are a reader. Taking a spare battery isn't a bad idea, actually.