Yes, I have. Though, I must say that most people have a different talking voice on the telephone than in person anyways. I know that I definitely sound different on the telephone rather than in person, and it is usually intentional. As for mechanics, perhaps it has to do with the quality of the phone and the receiver?
What do you do to sound different on the phone and why? I only alter the way I speak if I need to sound more "professional" or it's a clarity issue.
The timbre and pitch of my voice naturally sounds different than in person though.