Celebrities are commonly used as voice-over talent in advertising.  The common thinking is that celebrities can transfer their positive attributes (e.g. trustworthiness, familiarity, likeable) over to a brand.  This approach is no different when it is just the celebrity’s voice that is used in commercial.  Depending on whether brands want to come off as likeable, fun, authoritative, or manly, that can dictate the type of celebrity they will use as their brand’s voice.  Depending on the celebrity, their voice is instantly recognizable, such as Morgan Freeman in the VISA commercials, but often the celebrity lending their voice goes unrecognized.