In the tech-savvy city of San Francisco - teeming with commuters and tourists - the cellphone is a top target of robbers who use stealth, force and sometimes guns.
Nearly half of all robberies in the city this year are cellphone-related, police say, and most happen on crowded trains and buses.
One thief snatched a smartphone while sitting right behind his unsuspecting victim and darted out the rear of a bus in mere seconds.
Another robber grabbed an iPhone from an oblivious bus passenger - while she was still talking.
In nearby Oakland, city council candidate Dan Kalb was robbed at gunpoint of his iPhone last Wednesday after he attended a neighbourhood anti-crime meeting.
"I thought he was going to shoot me," said Kalb, who dropped his phone during the holdup. "He kept saying, 'Find the phone, find the phone.'"
The brazen incidents are part of a crime wave striking coast to coast. New York police report that more than 40 per cent of all robberies now involve cellphones. And cellphone thefts in Los Angeles, which account for more than a quarter of all the city's robberies, are up 27 per cent from this time a year ago, police said.
Thefts of cellphones - particularly the expensive do-it-all smartphones containing everything from photos and music to private e-mails and bank account statements - are costing consumers millions of dollars and sending law enforcement agencies and wireless carriers nationwide scrambling for solutions.
In San Francisco, police have gone undercover and launched a public transport ad campaign, warning folks to "be smart with your smartphone". Similar warnings went out in Oakland, where there have been nearly 1,300 cellphone robberies this year.
When Apple's iPhone 5 went on sale last month, New York police encouraged buyers to register their phone's serial numbers with the department. That came just months after a 26-year-old chef at the Museum of Modern Art was killed for his iPhone while heading home to the Bronx.
In St Louis, city leaders proposed an ambitious ordinance requiring anyone who resells cellphones to obtain a second-hand dealer's licence. Resellers would also need to record the phone's identity number and collect detailed information including the seller's names, addresses, a copy of their driver's licences - even their thumbprints.
"It will take a national solution to make this problem go away," St Louis Mayor Francis Slay said of the phone thefts.
In April, Senator Charles Schumer and New York police commissioner Ray Kelly announced that the major US cellphone carriers and the Federal Communications Commission had agreed to set up a national database to track reported stolen phones. It is scheduled to launch late next year.
Schumer also introduced a bill called the Mobile Device Theft Deterrence Act, which proposes a five-year prison sentence for tampering with the ID numbers of a stolen cellphone. The bill is supported by the Cellular Telecommunications Industry Association (CTIA), a Washington advocacy group.
In addition, CTIA officials said carriers were expected to launch individual databases later this month to permanently disable a cellphone reported stolen. The initiative is similar to a successful decade-old strategy in Australia.
Previously, US carriers have only been able to disable SIM cards, which can be swapped in and out of phones. That has led to a profitable black market for stolen phones.