Actually there IS a way eric, and in RL you can have an AM/FM turned on in your patrol car, but at low level... here's what you do, go to your gta install location default is c:/program files(x86)/rockstar games/ gta iv (OR EFLC if installed)/ common/data if you have the STEAM version c:/program files(x86)/steam/steamapps/common/GTAiv (i think) /common/data
find vehicles.ide, open in notepad, find the police cars you wish to enable the radio in and see a line like so
police, police, car, POLICE, POLICE, VEH@STD, VEH@STD_RI1, 100, 999, 0.2345, 0.2345, 0.2, 2, 1.0 ,1, ext_requi+ext_strong+livery
Change the red word to TAXI or something else, AM/FM radio is now active for that police car. you might have to save it non your desktop first then drag and drop into that folder. you also might wanna back up the orginal just in case