James Cameron once said:
"Somehow, even his accent worked. It had a strange synthesized quality, like they hadn't gotten the voice thing quite worked out."
The Sgt. Candy scene (see @Alenanno's answer):
In the Making of the Video Game from the Terminator 3: Rise of the Machines DVD, it is implied that this scene was filmed to be used as a cut scene, and not actually intended to be used in the theatrical release.
This would explain why:
This contradicts information from the first film, where Kyle Reese refers to the [Arnold model] as "new", replacing the older rubber-skinned 600 series, also seen in Terminator Salvation.
In the novel T2: Infiltrator a different origin for the physical and vocal templates was provided:
Dieter von Rossbach was a former counter-terrorist, who meets and joins forces with the Connors in the present.
The reason stated for copying Dieter was that Skynet was looking in the old military files for someone whose body could effectively conceal the Terminator's massive endoskeleton.