The latest free perk on U.S. airlines: Mobile messaging.

Delta Air Lines announced Wednesday morning that customers on its Wi-Fi enabled planes will be able to communicate via iMessage, WhatsApp and Facebook Messenger at no charge. Delta’s free messaging begins Sunday (Oct. 1) and will be available to customers whether or not they’ve paid for in-flight Wi-Fi access.

Delta says its move makes it the first of the USA's three big global carriers (American and United are the others) to offer the perk. But it's not the first overall. Customers on JetBlue, for example, already had access to free in-flight Wi-Fi, which would allow many of the same capabilities -- plus streaming and web-surfing.

And even without the same free in-flight Wi-Fi caveat, another big U.S. carrier -- an arch-rival of Delta -- already offered free mobile messaging. Alaska Airlines customers have had access to free in-flight messaging on its Wi-Fi enabled aircraft since January.

"We know that staying in touch while on the go is essential to our guests, many of whom don't need full Internet access,” Andrew Harrison, Alaska Airlines' chief commercial officer, said when announcing the chat option then. “Free Chat is a great way to keep that connection alive without breaking the bank.”

Alaska Air has since rolled out the complimentary messaging option to all flights on merger partner Virgin America, as well.

As for the effort announced by Delta announced on Wednesday, the company says it's "part of (a) multi-billion dollar investment in the customer experience." The move makes Delta the biggest U.S. airline to offer the option at no charge.

“We know many of Delta’s customers want or need to stay connected in the air and on the ground, which is why we’re investing in an easy, free way to send and receive messages inflight through some of the most popular global platforms,” Tim Mapes, Delta’s Chief Marketing Officer, says in a statement. “Coupled with our investments in seat-back screens, free entertainment and High-Speed Wi-Fi, free messaging is one more way customers can choose how to make the most of their time on Delta flights.”

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Delta says passengers will have the free messaging option on all of its Wi-Fi-enabled flights, a count that includes “all aircraft with two or more cabins.”

To access the option, fliers on Delta can unlock the option via the carrier’s Wi-Fi portal page. The option will allow text use only and will not support the transfer of photo or video files, according to the airline.

Delta also took the opportunity to tout its options for the more traditional seatback in-flight entertainment offerings. The company said it “offers customers more aircraft with seatback entertainment than any airline in the world, installing its 500th aircraft with seat-back entertainment in July.”

“In addition to investing in seat-back entertainment, customers can also choose to stream Delta Studio to their personal devices on the airline’s entire mainline fleet as well as all two-class regional aircraft,” Delta adds.

IN PICTURES: Behind the scenes at Delta Air Lines