Kevin Mercuri, 42, who owns a public-relations agency in New York, said he was parked in his Lexus in downtown Manhattan two months ago, e-mailing a client, when a police officer pulled up. Mr. Mercuri said he was in a legal parking spot but hadn’t fed the meter. The officer told him to move along.

“I explained I’d be out in 30 seconds, that I was finishing an e-mail,” Mr. Mercuri recalled. “The police officer, who seemed to be having a bad day, essentially started yelling at me. He forced me to stop typing. I drove two blocks and parked and finished my e-mail. I was blocking a fire hydrant.”

On weekends, said Mr. Mercuri, he drives to the suburbs to do errands at stores like Costco, where parking lots can get packed. He said that if he finds himself using his phone in his car after he shops and sees someone who needs his spot, he’ll pull into a fire lane. But on the weekdays, he said, he’s under too much pressure to give up a parking space.

“Monday to Friday, you have to have that hard edge,” he said. “On the weekends, I try to find small ways to do good to balance it out.”

On a recent morning in the crowded Noe Valley neighborhood in San Francisco, a string of people sat parked in cars talking, texting, e-mailing. Andy Murdock, parked in front of a bakery, sipped coffee and caught up by phone with his wife; Harold Trinkumas paused in a restricted zone in his BMW and dashed off a work e-mail, or tried to, when a garbage truck honked and nudged him along; Vik Singh sat in his spot and texted a good-luck message to a friend heading into dental surgery.

Mr. Singh, 31, said he took a vow about a year ago not to text or talk on the phone while driving. The reason? “Believe it or not, it was Oprah. She had that whole campaign,” he said, seeming sheepish.

And Sandy Kokesh, 56, a manager at Wells Fargo, sat in her Toyota while listening in on a work conference call. She needed to be in the neighborhood for another meeting but arrived early so she could sit quietly in the car and listen to the call rather than do so while driving, which her employer discourages.