Mobile Etiquette

I was surprised during my recent visit to India to see how ubiquitous mobiles have become. I am not talking about mobile telephony penetration but how many people are constantly talking, chatting, browsing on a mobile phone:

• People on two wheelers and cars in heavy traffic are regularly seen talking on the phone. They are not even on handsfree mode, either managing the motorbike with one hand or keeping the phone pressed between sholder and ear. 
• My friends, family, aquaintances regularly answer the phone even though we are in a middle of a conversation or a meal. 
• In public places people watch whatsapp or facebook videos without headphones, sometimes while listening to something else such as public announcement, flight security presentation, or television program.  

I will be shocked if I see any of this in USA, at least on the east coast where I have lived and worked. Some of these behaviors will be considered extremly rude.

While talking with a family friend, I realized that he finds answering mobile phone at all times obvious and American custom of not answering the phone immediately when it rings, rude and perplexing. What makes technology related customs develop in certain ways in certain places? Is it about the core cultural values or phase in technology life cycle? In India mobile phones were used as a means for urgent or emergency communication. Keeping a voice mail was unheard of. Even today few people think of leaving a voice mail or know how to.