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Delta Air Lines will soon test free Wi-Fi on some U.S. flights, a step toward a more expansive and permanent rollout of the service.

The Atlanta-based airline will offer complimentary internet connections to passengers on 55 domestic flights beginning Monday. The pilot program will run for two weeks to gather feedback and study passenger behavior when using the in-flight Wi-Fi.

There's no way for customers to know until the day of travel whether their flight will be included in the pilot as the routes will change daily. Delta said it will send customers on eligible flights an email or message through its smartphone app ahead of time.

"Customers are accustomed to having access to free Wi-Fi during nearly every other aspect of their journey, and Delta believes it should be free when flying, too," Ekrem Dimbiloglu, Delta's director of onboard product, said in a statement.

It's a tease of what's to come – though no one knows when or what exactly. Dimbiloglu said this won't be the last round of testing it does, adding that "getting this highly complex program right" is challenging. "This takes a lot more creativity, investment and planning to bring to life than a simple flip of a switch," he said.

During the experiment, passengers won't be able to use streaming services, like Netflix or Hulu, and will be limited to basic web searching, email, messaging and, of course, social media.

As internet connectivity becomes an increasingly assumed part of daily life, U.S. airlines have evolved along with it. JetBlue already offers free Wi-Fi, but so far, its domestic competitors haven't followed suit. Delta currently offers Wi-Fi on most all of its domestic and international flights, for a fee.

"As with any test in uncharted territory, Delta will rely heavily on customer and employee feedback to navigate how to best make free in-flight Wi-Fi a reality," Dimbiloglu said in a statement.

Delta has installed high-speed 2Ku on 60% of its mainline fleet. Customers will still be able to purchase Wi-Fi and use free mobile messaging during the test period.