The recommendation by the NTSB comes after an investigation into a crash in Munfordville, Ky. A tractor-trailer driver crossed a median and struck a 15-passenger van, killing 11 people, including two children.
The NTSB said the probable cause for the crash was that the truck driver became distracted while using his mobile phone, which had recently dropped a call.
While no state has an outright ban on mobile phone use by all drivers, the NTSB recommends that states adopt laws that would prohibit the use of handheld devices by commercial drivers, even if they have a hands-free attachment.
A recent study by the Texas Transportation Institute revealed that reading or writing a text message behind the wheel can more than double a driver's reaction time. It's safe to assume the results may be similar for drivers trying to dial a telephone, an action the NTSB said can have fatal consequences.
Texting while driving is currently banned in 34 states while using a handheld device in any way (presumably as a telephone) is banned in nine states. See a state-by-state list here.
Texas has attempted to ban texting while driving as recently as this past summer when both the House and Senate passed an ordinance prohibiting the act. Gov. Rick Perry vetoed the bill, calling it an "effort to micromanage the behavior of adults."
Still, Texas has passed two statewide laws regarding the use of handheld devices by drivers, and local municipalities have picked up the slack from there.
Statewide, Texas prohibits any driver from using a mobile handheld device while in a school zone unless it has a hands-free attachment. Additionally, school bus drivers, who must have a commercial driver's license, can only use a handheld device while driving a bus if there are no passengers younger than 18 in the vehicle. When passengers younger than 18 are present, the use of a handheld device, even with a hands-free attachment, is prohibited.
The NTSB said the only caveat to its recommendation is when the driver is in an emergency situation. See the full recommendation here.