The company is using "cell safety" to polish its responsibility reputation — paying for ads that explain the policy in the New York Times, the Washington Post, and the National Journal. ExxonMobil says the new policy will have a major safety impact on its employees and contractors, who collectively drive up to 1.5 million miles each day.

The company cited studies pointing to evidence that cell-phone use while driving increases the risk of accidents fourfold compared with drivers not using cell phones.

"We felt cell-phone use while driving was a fairly dangerous behavior," Mike Henderek, manager of safety programs for ExxonMobil, told the Cincinnati Enquirer.

The rule applies to 88,000 employees. ExxonMobil adopted the policy after assigning its own scientists to dissect the issue.

"The results verified that, while hands-free seems intuitively the right thing to do in terms of safety, it doesn't deliver significant benefit over hand-held," Henderek said. "It's the mind that becomes engaged in conversation and becomes distracted."