Libraries are associated with quiet. Even as recent as the last decade there was a library blog called Shush! (Can no longer find the site, although a Google search reveals the footprint.) Quiet is good. Silence is good. The modern library, however, is not quiet. People working together at computers, talking on cell phones, sharing media, perhaps a coexistence of quiet and activity, stillness and movement.
Personally I don't bat an eye (although sometimes I am a little jumpy) when someone's cell phone rings. It's a fact of life today, common as dirt. I swore I'd never be someone whose phone went off at an inappropriate time but that has happened.
Library users may want spaces where people can converse and engage and also spaces of quiet - when they want them. How to create space for both? The Librarian in Black pointed me to an interesting sign that might help library users modulate their sound contributions.