WiFi rarely comes cheap for airline passengers. But Delta is about to offer one form of connection at no charge: text messages. The airline said Wednesday that it would offer free mobile messaging on flights beginning Sunday. The service is “part of a larger strategy around entertainment and giving our customers something they’ve been asking for,” said Dan Csont, VP of brand management at Delta. Other airlines are expected to try to match the offer, but Delta could have an advantage, one aviation analyst said, because it has been investing heavily in equipment to help bolster its connectivity. “There will undoubtedly be attempts by other carriers to try to match this, but it comes down to whether they have the hardware to do it,” said Robert Mann, president of R. W. Mann & Company, an airline consulting firm. Delta said that passengers on all flights on planes equipped with WiFi from the broadband provider Gogo — which covers all but 130 small commuter planes out of the airline’s 1,300 aircraft — would be able to send real-time texts through the apps iMessage, Facebook Messenger and WhatsApp, including international trips. SMS texts sent through cell networks will not be allowed, per regulatory restrictions, the airline said. Delta trumpeted its service, saying it would be the first global carrier based in the United States to offer onboard texting without charging for online access. But some airlines already offer more than free texting. Since the beginning of the year, JetBlue has offered free WiFi, which passengers can use to surf the internet, stream content and communicate on chat apps.<br/>