JetBlue
JetBlue is the only airline that offers free Wi-Fi at every seat and on every plane. The airline partners with Viasat to provide Internet service. All JetBlue-operated flights have coverage over the contiguous U.S. and the airline promises high-speed Wi-Fi.
Southwest
Southwest Rapid Rewards members who reached the A-List Preferred status and Business Select Customers can use free inflight Wi-Fi during the whole flight. A-List members, other members of Southwest's Rapid Rewards frequent flyer program, and non-members will have to pay $8 for inflight Wi-Fi per device from takeoff to landing (texting with iMessage and WhatsApp is free).
Icelandair
Icelandair made Wi-Fi available to everyone on board of its airplanes. However, Wi-Fi access is not free for everyone. Thus, passengers flying Saga Premium and Saga Premium Flex receive complimentary Wi-Fi access for 2 devices. Icelandair Saga Gold frequent flyer members also get complimentary wireless internet for two devices.
Aer Lingus
Most Aer Lingus' A330 aircrafts have Wi-Fi (plus text and data) onboard, and all A321neoLR aircraft have Wi-Fi only. And all Aer Lingus flyers can get internet access starting at $3.99 for text messages only and at $24.99 for full internet access. Only Business Class customers and AerClub Concierge members can get Aer Lingus Wi-Fi for free.
Turkish Airlines
Wi-Fi connection on Turkish Airlines flights is available on an increasing number of international and domestic flights. Business Class passengers with Miles&Smiles Elite or Elite Plus Membership get the benefit of free unlimited Internet. Paid passes start from $5 for unlimited messaging and to $35 for unlimited internet on long haul flights.
Emirates
Emirates provides various onboard Wi-Fi plans for all passengers starting at $2.99. However, if you are an Emirates Skywards member, you can take advantage of free Wi-Fi services. Emirates Skywards members traveling in First Class or as a Platinum member in any travel class can enjoy free Wi-Fi internet for the whole flight.
Philippines Airlines
Philippines Airlines offers myPAL Wi-Fi Hi-Speed internet on select international flights. All Mabuhay Miles members have access to complimentary Unli Chat plan. Business Class passengers and Mabuhay Miles Million Milers are provided with a promo code to enjoy the 100MB plan for free. Additional Wi-Fi plans start at $9.98.
As you can see, sometimes even being a member of a frequent flyer program doesn't give you access to free in-flight Wi-Fi. Most often, you should be a business class traveler or buy the service onboard.