When Chin is talking to the native on Niihau, he puts his phone back in his pocket midway through the conversation. However, when the camera pans back to the woman, she has his phone again, giving it back to Chin as he walks back to Steve.
Despite the fact there is no cell service on Niihau, several members of Five O (Steve McGarrett and Chin Ho Kelly) are seen using their phones on the island.
Steve and Chin both received cell phone calls on Niihau. Chin mentioned earlier there are no phones on Niihau, and there certainly aren't any cell towers.