The plug: The average family of four uses about 1.6 gigabytes of data a month, according to Billshrink.com, though many pay $90 for 8 gigs. Track your usage to see if you can make do with a $60, 2-gig plan.
Nervous about overages? Use alerts or apps to keep tabs. Carriers have their own apps, or try DroidStats Android (free) or DataMan for iPhone (99ยข).