HOUSTON -- Harris County Jail inmates have racked up fraudulent charges on strangers' telephone bills by deploying a new tactic from behind bars, KPRC Local 2 Investigates reported Tuesday.

"What they're doing now is they're actually pretending to be someone from the Sheriff's Office," said Capt. John Martin of the Harris County Sheriff's Office.

The latest twist on the call forwarding scam has caught people by surprise in the past few weeks, including some who told Local 2 Investigates they fell for the scam despite having heard of inmate phone scams in the past.

Inmates have access to banks of pay telephones while locked in "day rooms" during daytime hours. They sometimes dial randomly, or deputies report they have found pages ripped from phone books where inmates search for new victims to pay for their calls to friends and relatives. If they can convince strangers to dial *72, it will forward the stranger's phone to a friend or relative of the inmate, while charges are applied to the stranger's phone bill.

"I believed it, I did," said Houston cosmetology instructor Wendy Brown. "He told me, 'Hi this is Officer Mack.' I immediately said, 'And you're calling from a payphone?' and he said, 'Well, I'm processing an inmate in.'"

The caller had an official tone to his voice and he told her an inmate had listed her phone number on a booking document, so he wanted to help her to reverse any fraudulent charges that may have been billed to her phone from inside the jail.

Brown said the caller was well-spoken and very business like, telling her, "OK, ma'am, well, in order to get these charges off your phone, I'm going to need you to write down some information."

He then told her to dial *72 and then a phone number, which he claimed would connect her to the official department that reverses fraudulent phone charges.

Authorities in Fort Bend, Grimes, and Walker counties also report Harris County inmates have begun scamming people in their rural areas who have yet to hear about the scam.

One Grimes County sheriff's detective told Local 2 Investigates he's hearing from new victims every day, including some who have lost hundreds of dollars.

"The scam itself continues to evolve," said Martin. "As people sort of get wise to what's going on now, they'll change it just slightly and so, over time, we see it continue to evolve."

He said the sheriff's office has posted information on its Web site to alert people to how the scam works.

"We're not going to make a collect call to relay (emergency) information to someone, so I would hope that that would clue somebody that this is likely a scam," he said.

Some victims have been charged for numerous inmate calls.

One woman who fell for the scam e-mailed Local 2 Investigates that she was successful in having her phone company reverse the charges. Phone companies can also place blocks on phone lines to bar any collect call from a jail cell payphone.