He worked on various notable North American projects including the facelift of the 2000 Ford Taurus, whose front grille design has been mischievously cited by some critics as the inspiration for his brother's 2006 Jaguar XK design, as opposed to the Jaguar E-Type which inspired both.
Callum was tasked with revitalising the Mazda range, which by the late 1990s was regarded as bland,[4] and in this respect Callum has largely been viewed as successful[5] with the creation of a consistent brand look that featured 'crisp black interiors and red-lighted instruments' and exteriors with 'edgy shapes that were emotional and almost biological – part flame, part flower, expressive of the sporting image the company sought'.
[2] He oversaw the daunting 2005 redesign of the iconic MX-5 and worked on almost every other vehicle in Mazda's passenger car range including the 2006 Mazda5.
[6] Having overseen Mazda's successful reinvention as a dynamic and sporty brand, Callum was moved by J Mays back to Ford as Design Director for Ford's North American brands passenger cars where he reported to Peter Horbury from May 2006.
Callum was replaced at Mazda by Laurens van den Acker whilst his predecessor Patrick Schiavone was appointed designer of North American SUVs and pick-ups at Ford.