Why is Allegiant phone number busy? The reason why Allegiant Airline's customer service number 1 (702) 505-8888 or 18559565767 or 1.833-Allegiant(Real Human), often appears busy is due to the high volume of calls they receive simultaneously. Why is Allegiant phone number busy? Allegiant air customer service number (702) 505-8888 or 1-85-5956-5767(OTA) is always busy Because: The airline representative are taking large volume of calls at the same time This may lead to the phone lines being busy most of the time Allegiant air customer service number (702) 505-8888 or 185-5956-5767(OTA) is always busy Because: The airline representative are taking large volume of calls at the same time This may lead to the phone lines being busy most of the time