On November 23rd, 2011, U.S. Transportation Secretary Ray LaHood announced a final rule specifically prohibiting interstate truck and bus drivers from using hand-held cell phones while operating their vehicles. The joint rule is a cooperation between the Federal Motor Carrier Safety Administration (FMCSA) and the Pipeline and Hazardous Materials Safety Administration (PHMSA) to end distracted driving.
The final rule can be accessed at http://www.fmcsa.dot.gov/rules-regulations/administration/rulemakings/rule-programs/rule_making_details.aspx?ruleid=324.
According to this FAQ, the effective date for the new rule is January 3, 2011: http://www.fmcsa.dot.gov/about/other/faq/cellphone-ban-faqs.aspx
According to the rule, the "use of a hands-free mobile telephone with a speaker phone function or a wired or wireless earphone" is allowed. For answers regarding the use of the push-to-talk function as well as CB and other radio devices, please see the above linked rule.
If you are involved in an incident and have questions, call the Leon Law Firm at 281-980-4529.