"No conversation" should be the default setting for any trip to a communal restroom. Chit-chat under these circumstances is inevitably awkward and takes you off the task at hand. A simple nod of the head or "Hey, how are ya?" when you encounter others along the way will suffice. This isn't one of Gertrude Stein's 1920s Parisian salons where painters, poets and novelists gather to sip wine and discuss life's endless possibilities. You may do your best thinking on the can, but that doesn't mean anyone wants to hear about it, at least not at that very moment.
And for God's sake, don't carry on a cellphone conversation in the loo. Not only is this annoying to others and unsanitary (apparently 16 percent of cellphones have fecal matter on them, according to Mashable), but you might end up dropping the phone in the bowl.