Boku has hired Mike Cahill as chief technology officer. Previously, Cahill worked at American Express where he was vice president of mobile engineering. And, prior to that, Cahill was Boku’s vice president of engineering. Based in San Francisco, Boku is a carrier billing-based mobile payment company. It is backed by Andreessen Horowitz, Benchmark Capital, DAG Ventures, Index Ventures, Khosla Ventures and New Enterprise Associates.