Did President Jacob Zuma, photographed seated, talking on the phone while shaking US President Barak Obama's hand at a UN leaders' lunch, cut short his call or did he not? Did he show the etiquette required of presidents or did he offend the sensibilities of one of the world's most powerful leaders.These questions are keeping social media abuzz.According to photographer Chip Somodevilla, who shot the image, Zuma was sitting at the table on Monday on his own, talking on his cellphone.Obama, unbeknown to Zuma, had entered the room and was coming up behind him, greeting other diners.He tapped Zuma on the shoulder as he walked past, and No 1 turned around with a big smile, stuck out his hand and shook POTUS's hand.POTUS, seeing Zuma still on his cell, gestured with his hand that No1 should call him when he was less busy.Somodevilla said Obama, who was "working the room" greeting world leaders as he approached the podium to make a toast, joked with Zuma when he realised he was on the phone."It was brief. President Obama was talking to President Zuma. You could see he was joking, making his hand into a phone gesticulating. They both had a very good laugh, before President Obama continued to greet other world leaders."Etiquette expert Danela Conti said the photograph would be a catalyst for cellphone etiquette debates."The image is almost too perfect. This, without a doubt, is going to be a talking point about the dos and dont's of cellphone etiquette."On the fact Zuma failed to stand up and greet Obama, Conti said regardless of who was greeting whom, one stood up, even in an informal situation like this."It is the proper etiquette."Former diplomat and Daily Maverick associate editor Brooks Spector said it was less a matter of protocol than a matter of good manners."This is an informal setting, but, having said that, my wife would have said: 'Put down that phone; we don't take calls at dinner'."..