Old School: A Universal Greeting

Yesterday, Wired pointed out one of the more simple inventions of Thomas Edison.  And it occurred yesterday 131 years ago.  Sure, Alexander Grahm Bell invented the telephone, but the wizard of Menlo Park came up with what we needed to really get the conversation started.   

Who gets the credit the for today's variations ("Yo", "'s Up?")?  Simple good ideas to put people at ease.