Need to hail a New York cab? Put down your aching, flailing arm and pull out your smartphone. The Big Apple is halfway through a yearlong “e-hail” pilot program in which prospective passengers can flag one of the city’s 14,000 licensed yellow cabs through three approved apps — Hailo, Uber, and Taxi Magic — available on iOS and Android mobile devices. Enter a street address or use your phone’s GPS to arrange a pickup. As of Oct. 1, Hailo users can even pay fares with their phones. For a small fee, riders who store credit cards and tip percentages in the app simply exit their cabs and receive instant electronic receipts.