Cell phone service plans and subscriptions usually consist of three parts: a voice plan, which covers incoming and outgoing calls, a text plan, which covers text and multimedia messaging, and a data plan. A data plan covers everything you do on the Internet -- browse the Web, download files, watch videos -- while using cell service.
Who Needs a Data Plan?
Cell providers don't usually require data plans for basic cell phones and feature phones. You might save money by buying a data plan rather than paying as you go, but basic cell phones tend to use very little data. Data plans are primarily targeted at smartphones, which can go through data very quickly. Even if you don't plan to use the Internet much on a new smartphone, you probably still need a data plan, as most carriers require a data plan to activate a new smartphone.
What Uses Data?
Most data plans provide a set number of gigabytes or megabytes, with overage charges if you use too much data. Cell carriers add up data usage from all your online activities for each billing period to see how much data you use. The biggest drains on data come from media, especially video streaming. Watching YouTube or Netflix can eat up hundreds of megabytes in just a few minutes. Even audio streaming apps such as Pandora and Spotify have a fairly heavy data footprint. Avoid these apps while on a cell connection if you have a low-end data plan.
Other online activities count as well, but don't have nearly as large an impact. Browsing the Web, sending email and reading Twitter or Facebook all use some data when performed over a cell connection, but unless you open a link to a video, you won't usually use more than a few megabytes at a time.
What Doesn't Use Data?
There's one major caveat to smartphone data use: data used while connected to Wi-Fi doesn't count. Android phones, iPhones, Windows phones and BlackBerry phones all offer Wi-Fi connections, and just like using Wi-Fi on a laptop, these connections have no relation to your cell carrier. Any time you can safely connect to Wi-Fi -- at home with a wireless router, in the office, at a restaurant -- you should. Once on Wi-Fi, it doesn't matter which apps you run or which sites you visit; your data usage won't rack up at all.
Apps that don't connect to the Internet never use data. Your phone's built-in calculator, for example, has no impact on data usage. Watch out for unexpected Internet activity, however: many free apps include ads, which will use up data if you aren't on Wi-Fi.
Track Data Use
To make sure you don't use too much data, and to decide whether you should change your data plan, monitor how much data you use month to month. The most accurate count comes directly from your cell provider: Log in to your account on the provider's website to see how much data you have left. Smartphones can also display data usage, but the numbers won't perfectly match the data your carrier bills you for.
The method varies from phone to phone. With an iOS 8 iPhone, for example, open the Cellular tab in the Settings app to see total data use and data use per app. IOS also offers switches to disable data use for specific apps. In Android 5, tap Data Usage in the Settings app and check the Mobile tab. For Windows Phone 8.1, tap Data Sense from its live tile, if one is configured, or from the App list.