Why don't you ask your local district attorney or prosecutor?
Or check Municode or
your state's government official website.
Georgia, for instance, allows for two-way radio, amateur and citizens band radios as well as what the code section defines as "functional equivalent":
'Wireless telecommunications device' means a cellular telephone, a portable
telephone, a text-messaging device, a personal digital assistant, a stand-alone computer, a
global positioning system receiver, or substantially similar portable wireless device that is
used to initiate or receive communication, information or data. Such term shall
not include a
radio, citizens band radio, citizens band radio hybrid,
commercial two-way radio
communication device or its functional equivalent, subscription-based emergency
communication device, prescribed medical device, amateur or ham radio device, or
in-vehicle security, navigation, or remote diagnostics system.
Functional equivalent=app used in a push to talk environment. Of course this would be an affirmative defense and won't stop someone from getting cited. It's all about how one handles themselves during a traffic stop and articulates both with the officer and if necessary, in court as to what outcome will occur.