“She came across as a lovely young girl, and I’m sure it wasn’t a nice feeling for the judge to send someone like this to prison  but someone is dead because of a text message,” said Bill Sykes, the officer who responded to the crash and led the subsequent investigation.

But many young people, among them the dead woman’s own siblings and friends, disagreed, sympathizing also with Phillipa Curtis. “I think Phillipa’s sentence was long enough, as she seemed like such a normal girl,” said Gemma Pancoust, the victim’s cousin and close friend, with whom she liked to sing karaoke to Dolly Parton’s “9 to 5.” “Until Tory’s death I texted while driving, as have most people. I don’t think she realized the danger she was causing.”

Indeed, the victim herself had sent a text message and talked on her cellphone (using the speaker function) while driving before her car broke down, according to the testimony of a friend with whom she had the 20-minute phone conversation. It is illegal in Britain to use a hand-held phone while driving, and drivers using hands-free phones may be fined if they are deemed not in control of the vehicle.

Although most European countries and a minority of American states now ban the use of hand-held cellphones while driving, Britain has become one of the more aggressive countries in attacking the problem, according to Ellen Townsend, policy director for the European Transit Safety Council, which advises the European Commission.

Britain’s new guidelines state that using a hand-held phone when causing a death will “always make the offense more serious” in terms of punishment and lead to prison time. Texting is given special treatment.

Ms. Curtis was found guilty and sent to prison even though she was not texting at the time of the accident, because the new guidelines regard “reading or composing text messages over a period of time” as “a gross avoidable distraction.” Its effect, British judges have ruled, may go beyond the moment of composing a message. Such behavior is categorized the same as driving while drunk or high on drugs, as well as racing another driver.

Image Prosecutors said the driver of the other car was distracted by texting.

On the night of Nov. 20, 2007, the victim, Ms. McBryde, was on her way to visit a friend when she got a flat tire at night on the highway.