I recently upgraded to an iPhone specifically for using it to help me learn languages. I kept seeing the new phones other people had (mine was a few years old already) and I was amazed at how far they had come and how practical they could be. I found that I had time between classes, before work, while waiting for the menu at restaurants etc., and any creative language learner knows that those are very valuable bits of time. This is where that iPhone can come in real handy. Of course this all applies to any smartphone, tablet, iPad or any similar device.
There are now tons of apps available for learning languages on your phone. Some are for free and many more offer expanded features and content for a fee, usually pretty reasonable. Some are from well-known reputable publishers of language learning products, like BYKI from Transparent Language or phrasebooks from Lonely Planet. Other apps can be produced by individuals, but may be just as helpful or cool. Some apps are offered as part of a subscription or account on a website, such as apps for Lingq or Anki.
There are plenty of dictionary apps that are available for free. Some have more features for a fee, like native speaker audio. Some apps have just a few thousand words but for dozens of languages. Having a dictionary of some kind is a no-brainer.
One of the ways phones are most useful is for news. You can get news from all over the world, for just about any language you are learning. This is mostly for intermediate or advanced learners, but there are a few news organizations that have news in simplified language. I have a few news apps for Spanish, and Le Monde for French. I can be reading the latest headlines from New York or Mexico City in Spanish, or Paris in French within seconds.
Just as the internet is a portal to the world, so is your phone. Searching for stations that are playing the kind of music or all-talk in the language you are looking for can be a pain (only because there are often so many choices!), but once you have found what you want, it is at your fingertips and your earbuds at will.
You can download movies and videos, of course, but YouTube is such an awesome source of material in such a wide variety of languages, that it is a must on any smart phone.
You can download lots of listenable content in the language you're learning, but you can also upload it from your computer or MP3 player. Spend a little time preparing some casual listening material and you will never be short of something to do in your new language.
Some people would think that spending fifteen minutes texting your friends in a foreign language is just goofing off and not very productive, but it's just the opposite. That's real life communicating in a foreign language, not verb charts and grammar rules and vocabulary lists. It is a training ground for proficiency and fluency. Hopefully, you can find some friends who speak or are learning the same language you are!
If your phone has a browser, you have access to internet sites either for learning languages, or in the language you are learning. This is especially helpful for intermediate and advanced learners, as you have an unending source of material to use.
There are plenty more ideas and uses for smart phones when it comes to learning languages. Just spend some time to set up your phone with a few apps, videos, music, news and whatever else you can think of. Think you don't have time to learn a language? Think again! Once you've prepared your phone, those few minutes you find here and there can become an indispensable part of your learning regimen!
"Language is the most imperfect and expensive means yet discovered
for communicating thought."
~ William James