Try this.
If the radio operator is set from the start, then just have it set so he can use radio command to execute your script. Get it? He has the radio, so he uses the radio commands?
Now what if it is a weapon you pick up from a ammo crate or a dead person?
In this case, were lookign at a two script operation. One your script you want the radio call to run, and two, a script to check and see if the player has the radio.
When the unti has the radio, then the trigger in the first script is triggered, and it exec the second script, then exits.
The second script creates the triggers/radio commands available ot the unit that just picked up the radio. It should also have a line in it that deactivates the radio commands form that player if they drop the weapon.
Now the guy with the radio hits the radio sequence to exec the script (or how many scripts/options/radio commands you want him to be able to choose).
I dont have time, but I'm sure you can find a Tutorial on how to make the scripts you need, or ask someone to help. In short, this is the easiest way to do this, and the most practical. Not to mention in my experience of trying ot do it, the only way that really works.