TripIt is a free service that simplifies organizing travel plans. The service has done an excellent job of making it painless to aggregate the collection of email receipts that you receive from airlines, hotels, car rental companies and travel agencies into one master itinerary. In order to use TripIt, you simply forward any email receipts to plans@tripit.com. The service extracts the reservation information from the message and assembles an attractive and very functional master itinerary from all the disparate documents. TripIt supplements the existing information with seating charts, information about local weather and events. Tripit supports a large number of travel-related vendors and regularly adds new ones based on demand.

I have been using TripIt for about a year and a half for both business and personal travel. TripIt provides many methods to access your travel information. There are three separate web-based interfaces–one for desktop browsers, one tuned specifically for the iPhone and one for other mobile web browsers. The service makes it possible to access your data via email, SMS, .ics calendar feeds and RSS feeds. TripIt recently added an Application Programming Interface (API) for developers that is rapidly expanding the number of options.

By default, trips are private. If you choose to add “connections” to other TripIt users, the service will then display trip basics including your destination and the dates you are traveling. You can choose to share trips and allow other individuals to view details such as flight and hotel information for a specific trip even if they are not TripIt users. You can also designate “collaborators” that make may changes or additions to an itinerary. While TripIt does have a number of social network features, these are not required to make the service useful for valuable.

Automatic account creation is one aspect of TripIt that illustrates how well email is integrated with the service. An account is created for you the first time you email TripIt a travel receipt. There is no need to go up through a separate sign up process, although you do have to assign a password the first time you log in.

One of my favorite talks from last year’s Web 2.0 Expo in San Francisco was “Making Email a Useful Web App” from Andy Denmark of TripIt. He made the argument that email is still interesting as an access point for web-based applications. He placed TripIt in a historical context of email driven applications such as the old email-based Internic domain registration forms. Denmark also mentioned TrackMyShipments, an online package tracking service, which is also email receipt-based. I like this service as well and will review it in the future.

The release of a TripIt developer API, immediately led to a number of useful connections to external service such as LinkedIn for sharing travel plans with business connections, Plaxo for integration with Plaxo Pulse and Plaxo Pulse, expens’d, which links with TripIt data to simplify travel expense reporting.

In some ways, TripIt competes with Dopplr, but in reality the services have minimal overlap and I think they are complimentary. Dopplr’s focus is on the social and visualization aspects of travel, while TripIt excels at many disparate travel documents and producing a useful master itinerary. I really look forward to the day when a developer connects these two services via their APIs.

I have very few complaints about TripIt, one is that it is difficult to retrieve older trips, which are sometimes useful when double checking records for expensing, etc. A brief history is available in the profile, otherwise you will need to find an old email from TripIt containing the URL from the trip to view the old itinerary.

The API connection potentially improves the situation for using your own historical TripIt records. That said, it would still be nice if TripIt created a way to easily view historical trips in the browser. This data is currently available in the calendar files and RSS feeds, but these are not convenient for most users to quickly look up a previous travel itinerary online. (Update: Thanks to a comment from TripIt’s Scott Hintz, I now see that the earlier trip history is available, just a little out-of-the-way. Thank you Scott.)

I have long wished that TripIt had a native iPhone application. The web-based iPhone interface is well done, but the master itinerary is also useful when I am without network connectivity such as on the plane or in a subway or when data is expensive such as on an international trip. This problem has effectively been solved with the release of the API as third party developers have begun to create applications that work with existing TripIt data.

There are now two travel applications for the iPhone that are able to sync with TripIt, FlightTrack Pro and TravelTracker. I have not yet seen applications for other mobile platforms such as BlackBerry or Android that will sync with TripIt data, but I would be surprised if the did not begin to appear up sooner than later.

The first application, FlightTrack Pro (iTunes Store link $9.99) is the big brother to the FlightTrack live flight tracking application. FlightTrack Pro can also synchronize flights with TripIt to automatically load upcoming trip information. The application includes features that appeal most to frequent fliers including arrival and departure times, aircraft type and flight maps. The application can download current information on flight status, any delays or cancellations and weather conditions over the air. FlightTrack Pro caches this information so you can review the details even after you are in the air and offline.

The second application, TravelTracker (iTunes Store link $1.99) is an iPhone application helps to track the large and small details related to travel such as airline, car and hotel reservations, frequent flyer account numbers. TravelTracker has a long heritage as it has been available for Palm OS since 1998. The application contains a number of internal databases including airports, Amtrak stations and a number of customizable shopping, packing and sightseeing list related to travel. TravelTracker includes the ability to keep track of expenses and includes a large number of default categories to select from. The application provides links to the internal browser to look up flight information, airport maps and seating charts.

TravelTracker provides several options for importing and exporting data. The application supports emailing itineraries as plain text, html or CSV. Users can independently backup or restore TravelTracker data via a desktop helper application. There were Windows and Mac OS9 desktop companion applications for the PalmOS version of TravelTracker. There is currently no stand-alone desktop applications that are compatible with the iPhone version.

The developer of TravelTracker makes a separate application called Flight Update ($5) that provides real-time flight information, which will hopefully also gain TripIt support in the future. If the user has them installed, TravelTracker would benefit from providing links to either Flight Update or FlightTrack as both are significantly more usable than switching to the built-in browser to look up information.

Third party iPhone applications are not allowed to access entries from the iPhone calendar, so neither FlightTrack Pro nor TravelTracker can place entries directly into your calendar on the iPhone. As a practical matter, this is not really a problem. TripIt provides its own .ics calendar feed that you can subscribe to from desktop calendars such as iCal or Outlook or from web-based calendars such as Google Calendar or the Hotmail Calendar.

* This article originally appeared as TripIt Shows the Value of Combining Email, Web and APIs in my Messaging News “On Message Column.” Minor corrections, URL, and pricing updates September, 13, 2010.