Verizon Wireless is spending nearly $3.5 million to update its Memphis-area switching station.

Every voice and data transaction of Verizon’s customers in the Memphis region passes through the station.

The nation’s largest telecommunications company last week applied for a building permit. The project will cost just under $3.5 million, according to the document.

“Verizon is renovating a portion of the facility … which is Verizon’s Memphis Network switch,’’ company spokeswoman Jeannine Brew Braggs told The Daily Memphian in an email response to questions.

She asked that The Daily Memphian not disclose the building’s address because of “security concerns.’’

“It handles all voice calls and wireless data transmissions for the region,’’ Braggs said. “The renovations will accommodate new technologies and the continuous increase in the demand for data for all customers.’’

Braggs had not responded to other questions about the facility by midafternoon Monday.

Three years ago, Verizon provided a rare tour of a switch station in the Pittsburgh area to a TV station with the understanding that the TV report not disclose the facility’s location.

According to the report by CBS affiliate KDKA, the switching station is off limits to most people. 

Employees there constantly monitor the system in case of issues, and the facility has backup generators and supplies should a power outage occur, KDKA reported.