Caps on wireless data plans may curtail streaming but not e-mail. By John Miley, Senior Associate Editor August 31, 2011 More smart-phone users face the monthly challenge of keeping tabs on megabytes and gigabytes as major carriers, including AT&T, T-Mobile and Verizon, substitute unlimited data plans with a slew of complex new pricing tiers. The networks say that few customers use enough data to exceed the new limits (for Verizon’s cheapest plan, that’s 2GB). But data use is skyrocketing: Tech giant Cisco Systems predicts that in 2015 the average user’s consumption will be 16 times 2010 levels. Surpassing your limit could bring extra charges or reduced network speeds. T-Mobile throttles connection speeds once data usage goes over the limit. Verizon and AT&T charge $10 for each extra gigabyte. Not all smart-phone activities are equal. You can send and receive a total of 10,000 plain-text e-mails along with 6,300 e-mails with attachments and still likely squeak under 2GB on AT&T’s network. The real data hog is video. Just five hours of high-resolution video could eat up 2GB. Streaming audio, Web-site visits, and music or app downloads are other data gobblers. Advertisement Each network handles data differently, which might affect usage counts. Most carriers have calculators on their Web sites to help you estimate usage. A Verizon customer with a 2GB plan, for example, could send 250 e-mails, visit 50 Web pages, stream 15 minutes of music and watch 10 minutes of low-resolution video every day for a month (total: 1.91GB). Most carriers let you change data plans at no cost. Switch to Wi-Fi when possible -- it doesn’t count toward your monthly tally.