Be that as it may, I conjecture that most of the annoyance is from people's instincts that they need to talk so loudly, especially when they have trouble hearing what coming out of the phone. In fact, shouting doesn't help at all and anything much more than a whisper doesn't really help.
http://pss.sagepub.com/content/early/2010/09/03/095679761038...
http://www.scientificamerican.com/podcast/episode.cfm?id=its...
And if flights are anything like Amtrak, people WILL take the opportunity to have 3 hour phone conversations when they're on a trip if they can.