What's the one app you can't live without?

Before 1999, a BlackBerry was just the name of a fruit.

And a few years ago, Apple launched a touch-screen smartphone that caught the entire mobile industry napping.

Soon after, there came an explosion of mobile-phone applications. From Facebook to Twitter and Maps to VoIP, there's an app for almost every imaginable activity. The phrase from Apple's iPhone marketing team, "There's an app for that," aptly describes what we've witnessed in the past year.

Now, what's the one application you can't live without on your smartphone? Tell us in Talkback.