Unlike minutes and text messages, which are relatively easy to quantify, understanding data usage isn't so simple. How many "megabytes" does it take to download a photo anyway?

An analysis by CUB and Validas, a Houston, Texas wireless software company, suggests that the average smart phone user consumes less than a quarter of the data included in his or her plan. This guide explains how data usage is measured, breaks down plans currently being offered by wireless companies, and helps consumers choose the best plan for them. A megabyte is a unit for measuring data. Whenever you send an e-mail, download a photo, or view a Web page, your phone is sending or receiving data. When it comes to cell phones, 1 MB of data is equal to roughly one of the tasks below: Even though typical customers use no more than 500 MB of data per month, many pricey data plans offer an even larger amount of capacity, measured by the gigabyte (GB). One gigabyte, which is about 1,000 megabytes, roughly equals one of the tasks below: According to Validas, consumers with smart phones—such as an iPhone, Android, or Blackberry—use an average of about 456 MB of data per month—far less than the standard 2 GB data plans pitched by cell phone companies. And 500 MB is no small amount. In fact, a quick analysis shows that it's enough data to send or receive 1,000 e-mails (100 with photo attachments), view 500 Web pages, download 10 apps, songs or games, stream 5 hours of music, and watch 90 minutes of YouTube videos.

In an analysis of more than 11,000 Verizon bills, Validas found that less than 4 percent of smart phone owners use more than 2 GB of data per month, and less than 1 percent use more than 5 GB a month.

Consumers with feature phones—phones that have access to the Internet, but are not typically used to stream video, music, or download apps—use an average of 30 MB per month, according to Validas. About 92 percent of feature phone users consume less than the lowest 75 MB tier offered by Verizon (T-Mobile offers a 200 MB plan), and nearly 100 percent use less than 2 GB of data.

These results are typical across the industry, so no matter what carrier you're with, be sure to check with it frequently, at least during the first few months of your contract, to monitor your data usage. You may be able to access your data usage info by texting your provider, logging into your online account, or downloading a cell-phone app. Below is a sampling of typical data plans currently available from wireless carriers.

Tethering allows you to connect your smart phone to your desktop, laptop, or other device, acting as a modem and allowing the device to access the Internet through your smart phone's connection. If you tether, be sure to monitor your data usage closely, as services like Netflix can quickly send you over your plan's data limit. CUB created this chart as a helpful guide to define what your monthly usage is. Prepaid wireless companies, like Boost Mobile, Cricket, and Straight Talk, offer unlimited talk, text and data plans starting at around $45 per month with no contract. While smart phones are available, you won't have your pick of the very latest models. For more information, read CUB's prepaid cellphone fact sheet. CUB calls on carriers to implement three reforms to better serve customers:

CUB is a nonprofit, statewide utility watchdog organization that was created by the Illinois Legislature. If you have a question or complaint about a utility, call CUB at 1-800-669-5556.