While a bell signals the end of the day for most high schoolers, students outside Norman Thomas High School in New York City line up outside a bright blue truck to hear their cellphones ring.

“All right, basically, when we come in the morning, we come to this truck and they hold our phones until we get out of school,” says Aaron Neil, a high school student who uses the truck. “And when we get out of school, we just come with a ticket that has our number, and we come and give the ticket in and then they give us our phone back.”

Ever since New York City banned electronic devices in public schools, a cottage industry has emerged: Charging kids a dollar a day to hold their phones during class. There are at least 11 storage trucks like this in the city.

“They have these trucks all around, all around New York, so they’ve got more than a thousand students going to this truck and they make mad money,” says student Randy Campbell.

The trucks frequent schools with metal detectors and strict enforcement of the cellphone rule. Some complain that unfairly takes money from lower-income kids. Others call them sitting ducks for robbery.

Edison Bardowell runs the nonprofit, Legacy Youth Corp, which owns two phone trucks. He’s trying to introduce a spirit of corporate responsibility to the industry.

“We feel it’s best to take a good percentage ­– 60 percent, 70 percent of the funds — and reinvest it into the school.  The school needs help,” says Bardowell. “The school needs extra funding for the programs, or the activities, or the training for the teachers.”

So far, Bardowell has raised $29,000 and hopes others will follow suit.