Passengers can quickly contact Allegiant! If they have any issues purchasing or reserving a flight, cancelling a flight, or changing the departure date. The passengers have a variety of ways to get in touch with Allegiant, so if you think like this, How do I call Allegiant customer service? So, To speak to a natural person at Allegiant, call "OTA": at +1-646-980-1956 or use one of the following methods.