I've done a lot of international travel this summer, and I have been using my iPhone as a substitute for lugging around a laptop. You can't do everything with an iPhone, but I did find it easy to keep up with my work files, my colleagues, my friends, and the local news while out of the office. Here are the apps that I found most useful when traveling.
- Mail. This is obvious, but the iPhone was great for reading and responding to e-mail.
- Documents to Go to view Word files. Like most law firms, my firm uses Microsoft Exchange for e-mail. Using Documents to Go, I was able to easily view Word files that were attached to e-mails that I received. Of course, Mail has the built-in ability to view Word files, but Docs to Go does a better job because you can adjust the font size and the app automatically formats the line breaks so that you don't have to scroll left and right to read the text.
- Documents to Go to edit Word files. Docs to Go also lets you edit Word files, and I used this feature quite a bit to markup edits to a Word file and then send the file back to my colleagues. Unfortunately, Docs to Go doesn't support the track changes features of Word, which would be an easy way to redline my edits. Instead, I made my edits to the document and then manually highlighted each of my edits in yellow and put the text in bold italics. That was enough to make my edits easy to spot for other readers.
- Foreign language dictionaries. There are a ton of these available depending upon the language that you need. Apps that allow you to hear the pronunciation of a word in a foreign language are especially useful so that you can hear how something is supposed to sound before you say the word to a waiter, store clerk, etc. I particularly liked the ViDICTO+ my trip series of apps which cost about $3 each and allow you to pick a category (hotel lobby, dinner, shopping, numbers & date, etc.) and see pictures that you can tap to see a foreign translation and hear the word spoken, plus hundreds of related phrases. You can currently get versions for Japanese, Chinese, Russian (the version I used), Spanish and German. This app didn't always have the word I was looking for, but I usually turned to this app first because when it was there, it was helpful. Another app I found very useful for Russia was SpeakEasy Russian. When you travel, you'll want to check the App Store to see what is available for the language that you need. For just a few dollars, you can have a great foreign language dictionary in your pocket that lets you hear exactly how to say a word.
- Maps. I kept my iPhone in airplane mode when I traveled to avoid data charges, but whenever I had access to Wi-Fi I frequently used the built-in Maps app to get a sense of my surroundings.
- Skype. I've mentioned this one before. If you are abroad and have Wi-Fi access (which is often easy to find in your hotel), you can use Skype to call home cheaply. I used Skype to participate in many hours worth of calls, including many long conference calls, for about $4 for all of the calls—cheap enough to be practically free.
- Social media apps. Using the Twitterific and Facebook apps, I was able to keep up with friends and family and local news even though I was far from home. The latest versions of both apps are excellent. I prefer the premium version of Twitterific which costs $3.99 and doesn't have ads, but if you don't mind the ads you can use the free version.
- Camera. With my iPhone 3GS, it was easy to take pictures and videos while out and about. Once I was in Wi-Fi range, I uploaded my pictures and videos to share with family and friends. I subscribe to Apple's MobileMe so I uploaded my pictures and video there, but I could have also uploaded them to YouTube. Or using the new Qik app, I could have uploaded video there. It was really fun to be able to share a video with people around the world just minutes after taking the video.
- Convertbot. Dollars to Euros, Celsius to Farenheit, kilograms to pounds, and many other conversions are easy with the Convertbot app. When I was in Russia I wanted to convert Rubles to Dollars, and unfortunately that currency was not supported, so instead I used the built in Stocks app and a trick that I described here to easily find out the current exchange rate.
- Weather. I always find it useful to keep an eye on the weather when I am traveling. There are many easy ways to check the weather using an iPhone, but I like the simplicity of the built-in Weather app (just add the cities that you will be visiting) and the iPhone-formatted version of the Weather Underground web page, i.wund.com.
- NetNewsWire. This is an RSS reader app that allows you to download the latest feeds from the websites that you follow. I love that I can launch NetNewsWire when I have Wi-Fi access and in under a minute download hundreds of posts from websites, and then later I can read the stories even if I am on a plane or in some other location where I don't have Internet access.
- DirecTV. If you subscribe to DirecTV, the company's iPhone app lets you record a program on your DVR so the show is waiting for you when you get home. I know that several cable companies have similar apps.
- Clock. This built-in app is a great alarm clock, just make sure that your ringer volume is turned up and the vibrate mode is turned off before you go to sleep. Also, the world clock feature makes it easy to see the current time at locations around the world. [UPDATE: as Florida attorney Keith Upson reminded me, the alarm will still make noise even if your phone is in vibrate mode. However, I have had a problem in the past where I had my ringer volume turned down and as a result didn't hear an alarm, so be careful with that.]
- Notes. This built-in app was a great place to jot down a note while I was out and about. Later on, in my hotel room, I would frequently use copy-and-paste to move what I jotted down to an address book entry, an e-mail, a calendar entry, etc.
There were other apps I also used such as iTunes to download new podcasts, apps from companies like the New York Times to catch up on the news, the iPod to listen to music and watch videos and a few games to pass the time. Put it all together, and the iPhone did a fantastic job of allowing me to keep up with my work files, stay in touch with colleagues, friends and family and keep in touch with the news at home even though I was abroad, plus allowed me to make the most of being in a foreign country.
[UPDATE: Rob Radcliff posted a comment below asking about data charges when abroad. I didn't research the exact fees, but articles like this one provide more information on these charges, which can really add up. If you have occasional Wi-Fi access when you are abroad, it is probably best to keep your phone in airplane mode.]
Click here to get Documents to Go ($9.99): 
Click here to get the ViDICTO apps ($2.99 or $3.99 each):
Click here to get SpeakEasy Russian ($3.99):
Click here to get Skype (free):
Click here to get Twitterific Premium ($3.99):
Click here to get Facebook (free):
Click here to get Convertbot ($0.99):
Click here to get NetNewsWire (free):
Click here to get DirecTV (free):
