What is it that the New York Times claims is causing teens anxiety, falling grades, repetitive stress injury and sleep deprivation? They claim teens are doing it at school, late at night, at restaurants and while crossing the street.

Spurred by the unlimited texting plans offered by carriers like AT&T Mobility and Verizon Wireless, American teenagers sent and received an average of 2,272 text messages per month in the fourth quarter of 2008, according to the Nielsen Company — almost 80 messages a day, more than double the average of a year earlier.

The phenomenon is beginning to worry physicians and psychologists, who say it is leading to anxiety, distraction in school, falling grades, repetitive stress injury and sleep deprivation.

Dr. Martin Joffe, a pediatrician in Greenbrae, Calif., recently surveyed students at two local high schools and said he found that many were routinely sending hundreds of texts every day.