The iPhone defaults to connecting via Wi-Fi when it's available, which helps you avoid running up data charges. If you need to get online while not near a Wi-Fi hot spot, however, the phone will connect using your cellular data plan instead. You can also temporarily disable Wi-Fi to force the phone to use a cellular Internet connection.

Disabling Wi-Fi

The iPhone will automatically switch to use a cellular connection -- such as 4G or LTE -- whenever it can't connect to a Wi-Fi router. If you need to manually switch from Wi-Fi to cellular, open the Settings app and tap "Wi-Fi." Switch the slider to "Off" to shut off the Wi-Fi radio. Until you change the option back to "On," your iPhone will only use its cellular connection for Internet data.

Downsides

In most cases, cellular connections run slower than Wi-Fi connections, meaning websites will take longer to load and files will take longer to download. Apple also places certain restrictions on cellular data. For example, you cannot download apps larger than 50 megabytes without using Wi-Fi. Unless you have an unlimited data plan, excessive Internet use can also result in additional fees.