While I have had some formal voice over training,
I learned to do the many-many voice's by help from my daughter.By that I mean,when she was growing up,she would ask me to put voices with her various stuffed animals she had accumilated via Dad,me.That plus the fact that I love to do different voices,it is something that comes pretty natural to me.It is my gift to make others feel good for lack of better words.
While taking choir in High School did help me in the ability to do various voices,I also have had some formal training through workshops,screen tests,and some acting classes.
I also took some drama in High School besides choir.
I believe in asking the client "how" he would like the read and the type of personality and/or
character to be.
The clients needs are number one,and should always remain as such.