I don't know what military technologies are available. But as a civilian, I can - quite easily - put together a system to do the following:
Find a way to implant an individual with an RFID/NFC chip that needs maybe a whole byte that needs reprogramming.
Within that implant would be precursors to chemicals that could turn the target into your own controlled potato.
The cellphone is critical. It has, within itself, a piece of hardware that has control over all the other hardware, controlled by the carrier. It also often comes connected to the user-facing operating system. We've seen it usually called "CarrierID" and we usually try to get rid of it.
Take a cellphone radio network technician who has the privilege to operate directly on the network, or hack it. Send the commands down to the cellphone. When the user has it up to their ear next?
Click.