Original: They were provided by Nicholas Briggs (who performed the voices for the Cybermen in Big Finish audio stories as well as the Daleks in both the new series and the audio stories).
Simplified: The voices for the 2006 return of the Cybermen were provided by Nicholas Briggs (who performed the voices for the Cybermen in Big Finish audio stories as well as the Daleks in both the new series and the audio stories).