iOS 4 is easy to use, but it’s also packed with features. That means the Settings app gets pretty complex—so complex that you’re bound to miss out on some terrific options. That’s why we’re highlighting four of our favorites that tend to go undiscovered. For starters, triple-tapping the Home button (toggle the triple tap on and off in Settings > General > Accessibility) can invoke accessibility settings—including our favorite, White on Black, which reverses colors on your iPhone screen. Aside from freaking out your friends, it’s great for low-vision users or anyone squinting at an iPhone screen in bright sunlight.

Mail’s settings can tweak the number of messages displayed, control font size, and more.

And if you stream lots of media, pay attention to the Cellular Data toggle in the Network screen. Flipping its switch to Off will keep your iPhone from using cellular data (surprise!), which is useful if you’re traveling internationally or just close to hitting your data cap for the month.

Improved Location Services settings are no longer all or nothing.

Mirroring Gmail, you can also opt to view email messages in a threaded conversation view. In Settings, tap Mail, Contacts, Calendars and flip the Organize by Thread toggle to on. While you’re in there, use the Minimum Font Size setting to beefup your text or fit more of your messages on screen.