Are you new to the iPhone? Welcome to the revolution! In 2011, Apple sold 72 million iPhones — meaning over 140 million of the popular smartphones have been sold since they were released five years ago! The iPhone is not only popular, it’s also incredibly versatile, with a whole host of apps to make it completely customizable.

If you’re browsing around the vastness of the Apple store for apps and don’t know where to start, we’ll give you a hint. Here are five essential apps for new iPhone users. These are the ones that everyone is using, so they’re a good place to get started.

1. Facebook

Obviously, the Facebook app is important if you spend any time on this social media site at all. The iPhone Facebook app features a clean interface that’s easy to use. You can do almost everything on the Facebook app that you can on the regular Facebook site, including search for friends or Facebook pages for businesses, leave comments and status updates, and even upload pictures directly from your iPhone.

2. Twitter

Twitter recently bought the Tweetie II app, and didn’t make many changes to it at all. That’s a good thing, since the Tweetie II app has always been simple to use and very versatile for Twitter users. The interface is clean, and you can pull a simple refresh mechanism to get the latest Tweets from all the feeds you follow.

3. Multi-Photo Email

This is a great app if you plan to take lots of photos with your iPhone’s awesome built-in camera. While you can transfer photos in other ways, email remains one of the simplest ways to send photos and to get them onto your PC, or a website where you can store them indefinitely. The regular email programs from iPhone can be somewhat limited, though, so the Multi-Photo Email app has stepped in to help. Now you can send multiple photos at once, making the process of getting those iPhone photos out there much simpler.

4. My Wallet

This is a great app to help you keep track of all sorts of information. Store the number for your cash back credit card with this app, or use it to keep track of information for your bank’s website or even for your Facebook account. My Wallet uses encryption to ensure that your information stays protected, but you’ll always have it with you to use whenever you need it.

5. Instagram

Your iPhone can already take some great-looking photos, but you can make them even cooler with Instagram. The photo editing app has a simple interface and adds filters to your photos. Turn your iPhone photos black and white, or give them a vintage look with a sepia filter. You can use Instagram to edit photos you’ve already taken with your iPhone, or you can take photos with Instagram’s filter already on. Instagram also makes it easy to upload photos to its own social sharing site or to Facebook.

The great thing about all these apps is that they are free or very cheap, so they’re a great way to learn how to use apps in general without spending a lot of money.

Once you’ve gotten the hang of these 5 essential apps, check out the app store to search through the thousands of available apps to find even more great iPhone apps that make your life simpler, more fun or more social.

Thanks to Stephanie Phillips for this guest post. You can e-mail her here.