It's pretty unusual and impolite, and also shows an ignorance of at least one of the functions of language.
As for which way to close a conversations, friends or close colleagues will use a normal Ciao (there is a recent custom of closing a phone call with a sequence of generally three ciaos). People who are in less intimate relation would say Arrivederci (even if A risentirci would be more correct), A domani (“till tomorrow”, if that's the case) etc.
Bye or words in other languages can happen, but it would be an unusual and joking way of speaking.
More or less all of the above (but for the thrice-repeated ciao) holds for meeting in person, for when you leave a shop etc.