A 'radio voice' means a voice that works well on broadcast radio, including those tinny portable AM radios. Any voice can be improved towards a radio voice with suitable vocal training.

A 'radio accent' is a bit different. The BBC is known to have it's own distinctive accent preferred for national broadcasts, in the past called [link|http://en.wikipedia.org/wiki/BBC_English|BBC English]. The Tennessee TV producer I mentioned before called it TV accent, which meant something essentially neutral and understandable by the whole country.

Wade.