Is it normal, to talk in different voices on the phone?

At some point during my childhood, I noticed that my mother would talk in different voices when on the phone. If the call was from someone similar, like her mother or her father, she would talk to them in the same real and casual voice that she would use when talking to me. However, if the call was from someone she didn't have a personal relationship to or knew, she would use a different voice. She would also use this voice when making important phone calls. The voice is very different from how she normally talks. It is hard to describe but it has more of a pep and happy tone to it and it is done with a lot of smiling. I think that I once asked her why she did this, but I don't recall her ever giving me an answer…

I am adult now and sometimes I am required to make phone calls, even though I hate doing so, and I've noticed that I too use different voices. I find this all to be very curious and strange. Is this a normal thing to do? Do you it too?