OK, but without me detailing how to do it.
Without me detailing how to do this, can I supply an answer for you? My background involves 2-way Cellular pager systems and not what you think. I have been on the design teams that designed the computer boards and radios that sit behind the antennas. What I know is that such systems are not that secure and I'd like to get you an answer you can use. But it I'll repeat it again. I can't in good conscious write how to do this in detail. I can share what it's called and supply an article about it.
Maybe someone will but I want no part in propagating this problem.