(ShareCast News) - Advertising giant WPP has taken a minority stake in Australian media agency Rapid Media Services. In an announcement Sir Martin Sorrell's WPP said the media planning and buying firm had already been affiliated with one of its media agencies, MediaCom, since 2001.Rapid Media Services would continue to operate as an independent business, operated by managing director Vaughan O'Connor.WPP's announcement did not disclose financial details of the deal.