Oh, in case you have mis-placed your copy of Debrett's New Guide to Etiquette and Modern Manners then here is a handy linkage to their guidance on Mobile Phone Etiquette.
We must always remember that Debrett's is the modern authority on all matters of etiquette, social occasions, people of distinction and fine style. And also remember that The Queen gives a copy to all her children each Christmas so that they are on best behaviour when she is not around to supervise.