NQ Mobile Vault is the simplest application I've seen for keeping text messages, call history, contacts, photos, and videos private on your mobile device. Celebrities, pay attention.
Basically, Vault creates an encrypted, password-protected space on your device, in which you can store photos, videos, text messages, and call history. It's easy to move items into and out of the space, and you can even permanently delete them, if you'd like.
Once you create your password, there are a few ways to start using Vault. First, within the app, you can pull up all of your messages and calls, and mark the individual items you'd like to add to your vault. If you want to hide all of your correspondence with a particular individual, just add him to your Private Contacts list. This will automatically hide any future messages or call history (except for notifications) with that individual as well. And just as easily, you can go through and hide any of the photos or videos stored on your device. To remove an item from your vault and put it back on your phone, long press and hit Restore.
One of the coolest of Vault's features is Stealth Mode. Available only to Premium users, Stealth Mode hides the application from Android's app drawer, so no one can see that it exists. In order to access Vault from Stealth Mode, you must open your phone's dial pad, input "##" followed by your Vault password, and press Call. In fact, this dial pad shortcut works even if Stealth Mode is not enabled.
Another premium feature available is the Break-in Monitor. When enabled, your device will undetectably snap a front-facing photo anytime an incorrect Vault password is entered. Then, the next time you open your Vault, the app will notify you of all such break-in attempts.
Lastly, premium users also get the ability to create multiple vaults. With this feature, you can create a "fake" vault for use in case someone unexpectedly demands to see what you're hiding.
With its supersimple interface, encryption technology, and powerful features, NQ Mobile Vault is one of the neatest apps I've seen. The free version is great for keeping photos, videos, or correspondence private, and the premium version (with monthly fee) offers even more powerful features, like a Break-in Monitor and Stealth Mode. Whichever version you choose, if you're looking for a sort of privacy locker for your phone, I'm confident you won't be disappointed with NQ Mobile Vault.