Celia Williams, former executive producer at L.A. music house Endless Noise, has joined Arnold/N.Y. as head of broadcast production, where she will report to executive creative director -- and fellow DDB alum -- John Staffen. ... Freelancer Philip Bonnery and Alex Flint -- formerly of Spike DDB -- have joined Boston agency Modernista! as a senior art director and senior copywriter, respectively. ... Reid Thompson, formerly a lead designer, has been promoted to creative director/designer at Hollywood's Troika Design Group.