FORTUNE -- Next time you whip out your iPhone on the sidewalk or the subway, you might first want to glance over your shoulder. Smartphones have become a favorite target of thieves who do what the police call a snatch and grab. One favorite M.O.: The perp grabs a phone and jumps off the train just as the doors are closing. So far this year, over 40% of thefts in New York City have involved cellphones, with a record 11,000 estimated to be lifted this year.

Sadly, this is largely preventable. Yes, AT&T (T) and T-Mobile will cancel your SIM card after a phone is reported stolen to protect personal information, but any thief can just slip in a new SIM and resell the phone on the black market. Sen. Charles Schumer (D-N.Y.) just launched a campaign to get the carriers to shut down the phone itself remotely. Verizon (VZ), Sprint (S), and many European carriers already do so. Consumer Reports notes that nothing technical hinders AT&T and T-Mobile from rendering their phones useless: "It's a simple decision that so far they're not willing to make." AT&T will say only that it adequately protects its customers' privacy. T-Mobile won't comment. In the meantime, hang on tight to your phone.

This article is from the October 17, 2011 issue of Fortune.