Tech-savvy consumers have come to expect wireless Internet access in many of the places they go - from coffeehouses to McDonald's to the public library. But aboard planes? That's a different story.

Airlines have been talking for years about adding Wi-Fi to flights, but the rollout has been slow, and adoption by passengers even slower.

Today, only about half of U.S. mainline aircraft -- which excludes small regional jets -- offer in-flight Wi-Fi service, generally at prices of US$5 to US$13. Even when it is available, only about 7 percent of passengers are logging on at 30,000 feet.

Chicagoans, in particular, can be forgiven if they're unfamiliar with in-flight Wi-Fi. Chicago's dominant carrier, United Airlines, doesn't offer Wi-Fi on any Chicago flights. The next-largest Chicago carriers, American Airlines and Southwest Airlines, have equipped only parts of their fleets with the pricey equipment needed to offer airborne Internet access.

Nationwide, about 1,800 mainline aircraft out of a total of 3,500 are equipped with Wi-Fi, said Amy Cravens, a senior analyst at market research company In-Stat.

So, the vision of the business traveler maintaining constant contact with the office while flying -- or the leisure traveler tweeting, Facebooking or checking fantasy baseball stats in midair -- has not been realized.

But that's soon to change. Sky-high Wi-Fi might finally be coming of age.

United Airlines announced in recent months that it plans to begin equipping its entire fleet with satellite-based Wi-Fi offered by Panasonic Avionics Corp. United will start the project during the second half of this year and plans to complete it by 2015. United is the largest airline in the Chicago market, accounting for more than one-third of all passengers who use Chicago O'Hare or Midway airports.

United opted to go with satellite-based Wi-Fi so all planes would be similarly equipped and could maintain connections across country boundaries, whether the planes were flying domestic or international routes, spokesman Rahsaan Johnson said. "We wanted a system that would work for customers no matter where they were in the world," he said. The airline did not announce pricing.

Last month, US Airways announced it was expanding its in-flight Wi-Fi provided by Itasca-based Gogo, far and away the largest provider. The airline, which has equipped about 60 percent of its fleet with Wi-Fi, said it will have 90 percent of its planes equipped by the end of 2013.

"We're not there yet, but we're heading in the right direction," Cravens said. "In the next couple of years, I think it's going to be much more available than it is now."

Southwest Airlines, Chicagoland's No. 3 carrier, has about 207 planes -- about 37 percent of its fleet -- equipped with satellite-based Wi-Fi. It's provided by Row 44 Inc., which is based in California but has a large office in Lombard. "We're equipping another of their planes every few days," said Robbie Hyman, spokesman for Row 44.

American Airlines has 328 planes equipped to offer wireless Internet, en route to its goal of 400 by the end of this year, which would raise the portion of its fleet with access from 67 percent to 82 percent.

Delta Air Lines offers Wi-Fi on all its mainline planes and many of its regional jets. AirTran, now owned by Southwest, and Virgin America have equipped their entire fleets, and Alaska Airlines is almost completely outfitted.

From a business standpoint, the installations might be coming none too soon.

Airlines that have been slow to add Wi-Fi are losing small amounts of market share to those that offer it on most or all of their flights, said Henry Harteveldt, co-founder of Atmosphere Research Group.

Customers won't choose an Internet-enabled flight over one that has significantly better fares or flight times. But all else being equal, Wi-Fi can be a tiebreaker, he said.

"Wi-Fi can be the cherry on the icing on the cake," Harteveldt said. "That's especially true for people who are in sales or consulting, where time literally is money. These guys want -- and need -- to be online."

Part of the reason for slow Wi-Fi rollout is that it's expensive for airlines. While home Wi-Fi might only need a US$50 wireless router, equipping a single plane with air-to-ground Wi-Fi capability can easily cost US$100,000. Satellite-based systems, such as those offered by Row 44, can cost double that. It's also costly and time-consuming to take a plane out of service to retrofit it with Wi-Fi equipment.

"Facing fuel that soared in price and now accounts for between 40 percent and 50 percent of their expenses, airlines are very careful about making any kind of major capital investment," Harteveldt said.

While airlines have been avidly talking about adding Wi-Fi since 2008, passengers are more interested now because they are more likely to have wireless-enabled gadgets, Harteveldt said.

"You've had an explosion of Wi-Fi capable devices, especially smartphones and tablet devices, which were just beginning to come on the market in 2008," he said. "As a result, you now have more and more people capable of using the system."

Adding Wi-Fi became a chicken-and-egg situation in which airlines didn't want to invest in Wi-Fi until passengers demanded it, but passengers didn't demand it until they had wireless devices and knew the service was regularly available.

As a result, just 1 of every 15 passengers who could access the Internet in-flight were doing it, according to In-Stat.

Another reason for slow adoption of Wi-Fi by passengers is they view it as too expensive. For a flight of more than three hours, passengers are willing to spend an average of US$4.46, according to data collected by In-Stat. However, Gogo, the dominant provider in the United States with about 90 percent of the market, generally charges US$12.95 for laptops on long flights.

"I think there is a disconnect in terms of value perception and where the service is priced," Cravens said. It doesn't help that it's a hassle to use - pulling out a credit card and typing in the number to gain access. "When people are on the fence already, things like that prevent usage. I think that's been a barrier."

Now pricing is changing, as Gogo experiments with different schemes.

"Gogo has only recently come out with what I would call popularly priced options," Harteveldt said. "For example, now you can get a 15-minute pass to check email on short flights for US$1.95." A Gogo spokesman declined to speak publicly about the company and pricing because it has filed for an initial public offering of stock and is in a so-called quiet period.

Southwest Airlines is different from others because it sets its own Wi-Fi rates. It has maintained a flat fee of US$5, regardless of flight length or device.

Another price-related factor is that consumers are becoming accustomed to free public Wi-Fi - not only in Starbucks and McDonald's but in many airports too. "That makes it harder to ask for US$10 on the plane, when it was just free in the airport," Cravens said. "Even though it's a completely different service and the cost structure for the providers is totally different, from an end-user perspective it's no different - and they don't understand why they have to pay."

Yet another issue with the value proposition is the battery life of devices. A passenger might consider paying US$12.95 for four hours of service during the flight. But if she knows her laptop battery will die after just 90 minutes, the service becomes more expensive per hour. "In that case, there's no more value than on a shorter flight, where pricing is lower," Cravens said.

For some passengers, that challenge will continue to be an issue until airlines increase availability of electrical power in seats so passengers can plug in devices. However, many of the newest smartphones, tablets and laptops are coming with much longer battery lives, which can make paying for Wi-Fi seem like a better deal. The new iPad 3, for example, claims a battery life of up to 10 hours.

Ultimately, the biggest boost to greater adoption will be greater availability.

Travelers will come to expect it, Cravens said. "When it's anticipated, it's used more," she said. Cravens said she expects the current 7 percent adoption rate to increase to 10 percent this year.

"Some airlines are getting to the point where you can pretty much expect to have it available. It just depends on who your preferred airline is," Cravens said. "All the major airlines in the U.S. are implementing the service. ... It's just a matter of time."