Air-to-ground telephone calls made by airlines are subject to the Illinois Telecommunications Excise Tax when the calls originate or terminate on equipment that is located in Illinois at the time of the call and have a bill for services that is sent to an Illinois address. A company plans to offer airlines wireless Voice over Internet Protocol (VoIP) telephone service which allows airline personnel to place and receive calls using a Wi-Fi signal from an aircraft in flight to and from other airline personnel at various ground locations. Airline personnel are provided handsets that are assigned an area code and prefix associated with the company’s Illinois data center. When calls are made, both the caller and the equipment might not be in Illinois. The Telecommunications Excise Tax is imposed on the amounts charged to the customer’s service address for the act or privilege of originating or receiving telecommunications in Illinois and for all the services and equipment provided in connection with by a retailer. For air-to-ground service, the service address is the location of the taxpayer’s primary use of the telecommunications equipment as defined by telephone number, authorization code, or the location in Illinois where bills are sent. The assignment of a telephone number to equipment that is associated with a central office in Illinois, alone, is insufficient to impose the Telecommunications Excise Tax. Therefore, the Illinois Telecommunications Excise tax will not apply to all services provided under this contract. Rather, specific sourcing must be applied based on where the aircraft is at the time it places the call, the ground facility called and whether the bill is sent to an airline in Illinois. (Private Letter Ruling ST 10-0005-PLR, Illinois Department of Revenue, August 9, 2010).