engagement-checkupiPhone users know that not all apps are created equal. There’s the “web app,” which is essentially a web page formatted for Apple’s mobile devices. Then there’s the “native app,” which customers can download from the iTunes store. These apps live on the smart phone itself and can be accessed without connecting to a web browser.

So, if you’re an airline, you can develop a unique app that allows passengers to purchase tickets, access their boarding passes, track flights, and receive inflight messages without touching a printed slip or clicking a mouse.

Sounds like a no brainer, but so far only a few airlines have done it.

British Airways led the way in July 2008 with a free app aimed at frequent flyers. Australian-based Qantas soon followed suit. Then, this summer, Air Canada became the first North American carrier to launch an app that lets passengers store their flight info, check the weather and even rent a car through their iPhones. (Though unfortunately these apps are only available for download in their native countries, so that a Canadian flying to Sydney won’t be able to grab the Qantas app until he’s down under).

Since then, American Airlines, Delta Air Lines, EasyJet and others have released web applications—and several carriers, including SAS Scandinavian Airlines, offer mobile boarding passes— but the list of airline-branded native apps remains startlingly sparse.

It’s surprising because awesome travel-related apps abound. Check out this list of iPhone apps for airline geeks, which highlights applications devoted to everything from airport codes and airplane seating charts, to flight tracking and aircraft specifications. Meanwhile, augmented reality applications like Layar and apps from travel brands like Kayak and Lonely Planet are cornering the Transumer market.

Airlines might consider forging virtual partnerships with other iPhone-friendly brands and independent developers. Virgin America has already sponsored the popular itinerary-planning app TripIt. Now imagine if Guinness’ Pub Finder tool lived within an Aer Lingus app—both of which were integrated with Layar.

If airlines won’t be developers, they can still be facilitators, connecting brands and Transumers throughout the journey cycle. Travellers crave useful content in their medium of choice and if airlines don’t provide them with it, someone else will.