Alexander Graham Bell
He was a scientist, inventor, engineer and innovator who invented the first practical telephone.
What is the difference between formal and informal telephone conversation ?
The language used for speaking on the telephone is very similar to that of ordinary conversation, but it is up to some special situation,for example a restaurant reservation, get information,etc.
1.  I think the most important difference is that, in a formal conversation we mention to the most important and main points of matter of conservation.
2.Another difference is that in formal conservation we use formal and official words but in  informal conversation, we no need to use the official and formal words, and it may be a friendly conservation.
3. An informal telephone conversation is usually between friends or informal persons but a formal telephone conversation is between official persons ,persons who have responsibilities, bosses and etc.
Thanks and have a good day.

As a practice I called 416-393-7131 to get some information about Toronto Public Library's special service known as Home Library Services. It needed to press number 4 in my cellphone. I found that Home Library Service is available for Toronto residents who are housebound for three months or longer due to age, illness or disability. A variety of library materials, including books, paperbacks, large print books and talking books, are selected and delivered to them free of charge.
I think it is amazing!