If your carrier doesn't offer a data usage app, or if you want an app that has more features, is a free data-monitoring app for Android that lets you do the usual--set a data cap, see a breakdown of which apps use the most data, and see how much data you've used in any given cycle. Onavo also employs proprietary algorithms to analyze your data usage and let you know whether your data plan is a good fit for you based on that usage (the default Android data usage tab does not analyze usage). Most of these features are also available as Android home-screen widgets that make it easy to monitor data usage at a glance.

Here's a quick and easy way to cut data costs: If you're not using all of your data each month, move to a lower plan. To determine whether you should move to a lower plan, either analyze your data usage for a couple of months using the aforementioned data-usage apps, or calculate how much data you'll need with a usage calculator.

During PCWorld's , we found this from Verizon Wireless to be fairly accurate at determining how much data we needed per month. You can also find data usage calculators at other carriers' sites: , , and .