If you upgraded your iPhone, iPod Touch, or iPad to iOS 5 last week, there’s a good chance you didn’t notice an incredible new system-wide feature that can turn your device into a productivity powerhouse: Text expansion!

We’ve already told you how amazing text expansion can be on a computer, but it’s even more useful on a phone with a tiny touchscreen keyboard. If you’re unfamiliar, text expansion is the process by which short, custom phrases can be expanded into full words or sentences, automatically. For example, I set up my phone to print “HackCollege” whenever I type “HC” (suck it, HerCampus). If you take the time to become cognizant of words you type frequently on your iPhone, this process can quickly add up to a huge time savings.

You could use TextExpansion before on iOS devices, but only be in the form of apps that forced you to copy your finished text to the clipboard to use elsewhere. Mercifully, iOS 5 enables the functionality in any app, at any time. To get started, head to Settings > General > Keyboard. At the bottom you’ll see a “Shortcuts” section with “omw -> On my way” filled in as an example. Click the button below that to add a new shortcut, fill in your full phrase on the top line, and the shortcut below, and it will be enabled system-wide.

You can also add phrases without shortcuts to include them in the system dictionary. This can keep the phone from auto-correcting the name of your dorm building or dining hall to something random. You can also teach your iPhone all types of colorful swear words, a welcome relief for any iPhone-toting potty mouth.

Text expansion and custom dictionary words aren’t going to let you type out a term paper on your 3.5 inch screen (though I once typed a four pages on my iPhone while sitting in a waiting room), but they can be tremendously helpful for speeding up your text and email replies, as long as you diligently add common phrases to the dictionary.

What are some of your other favorite iOS 5 secrets? Let us know in the comments!