Hailo, one of a growing number of companies using smartphones to dispatch taxis in Boston, has received $30.6 million in funding to expand its service across the United States and globally.

Among the new investors in the London company is Richard Branson, the billionaire chairman of the Virgin Group, and the New York firm Union Square Ventures, one of the early investors in the social media network Twitter. They are making a big bet that consumers will increasingly use smartphone apps to hail cabs instead of waving down drivers on the street or calling dispatchers.