Character voices have been a part of my life before I knew what they were called. It's simply natural for me. I started as a kid mocking everyone that to me had a different way of speaking. I believe that is what makes me sound natural and not forced.
I have provided the voice over for an invention sent to a marketing convention and I've done a couple of demo's, one of which I provided to my acting coach while attending John Robert Powers School.
Every day is like non stop practice. Going up to strangers and speaking with a different accent or using a different accent on the phone and afterwards asking them if it was believable. So far I've only had positive responses.
My training came from life itself, but I did go to John Robert Powers school to get training in cold reading techniques,monologues,commercial study,sit coms and t.v.