BlackBerries also are the subject of a more than four-year-old patent infringement lawsuit that could end with BlackBerry users being in the dark - a BlackBerry blackout.
A key hearing on the suit was held Friday in Richmond, Va. The federal judge presiding over the case did not issue a decision after the hearing ended Friday afternoon.
Sargent works as a property manager in Hagerstown for Hagner Management Inc. He uses his BlackBerry as a cell phone and for e-mail purposes.
"I find myself tapping out e-mails when I'm driving down the road, which I'm sure will be illegal soon," Sargent said.
He also can review rental leases while out of his office, and had GPS software installed so he can obtain directions.
Sargent is one of more than 3 million BlackBerry users in the United States.
Sam Cool is another.
Cool, who lives in Hagerstown and works outside Washington for a technology company, uses his BlackBerry to check his e-mail and keep track of his calendar, among other tasks.
"I'm addicted to it, the old 'CrackBerry,' or whatever they say," Cool said.
"Every waking minute," is how often Cool uses his BlackBerry, he said. "From the moment I get up until I go to bed."
He has had a BlackBerry since 1999 and recently upgraded from a much smaller, older model. The device allows him to surf the Internet and has games on it, including a Texas Hold 'Em poker game.
Cool said he does not use his BlackBerry as a cell phone because of provider issues, but prides himself on quickly responding to e-mails.
Like Sargent, he can multi-task.
"I can type on it without looking at it while driving," he said.
Without his BlackBerry, Cool said, he would be forced to carry around his laptop more often. He is vice president of networking and convergence for Germantown, Md.-based Planet Technologies.
Both Cool and Sargent said they do not expect BlackBerry service to be shut down as a result of the patent infringement lawsuit, with Cool saying he would be "surprised and amazed" if service were interrupted.
Sargent based his confidence in part on his brother, who works as a speechwriter in Washington and has witnessed firsthand the device's popularity with lawmakers. BlackBerry's federal government contracts, he believes, will prevent a BlackBerry blackout.
The Web site for BlackBerry states that customers include government employees on local, state and federal levels, as well as people in the fields of finance, health care, law and real estate.
Miscellaneous companies with employees using BlackBerries include the NBA, Universal Studios, Royal Caribbean International and PepsiCo, the Web site indicates.
If the federal judge issues an injunction on U.S. sales and service of BlackBerries, government and emergency workers would be exempt.
The BlackBerry hit the market in the late 1990s, becoming popular with professionals who wanted to check e-mails away from their office and home computers.
In 2001, Arlington, Va.-based NTP sued Research In Motion Ltd. - the company that makes BlackBerries, for patent infringement. NTP was co-founded by the late Thomas Campana Jr., an engineer who in 1990 created a system to send e-mails between computers and wireless devices. He is survived by his wife, who owns a large stake in NTP.
In 2002, a jury sided with NTP and awarded the small firm 5.7 percent of U.S. BlackBerry sales, a rate that U.S. District Judge James Spencer later increased to 8.55 percent.
Spencer issued an injunction in 2003, but held off on its enforcement during RIM's appeals. Those efforts largely failed and the case returned to his court last year.
Should sales and service be halted, Canada-based RIM executives say new software has been created for BlackBerry users that will prevent any service disruptions, but they have released few details. Some analysts are questioning the viability of the workaround and whether it might inconvenience users or degrade service.
The Associated Press contributed to this story.