Hz of Ghz
I doubt the transmission frequency matters much because it's way beyond what a cell can directly interpret. What I would expect to matter is the packet rate, which is in the milliseconds range. A constant transmission may do nothing more than slightly alter some chemical thresholds in some insignificant manner. Modulating the transmission with a low frequency could modulate those thresholds in a way that generates biologically significant signals. It's similar to how a cellphone makes an audio amplifier buzz. The audio amp's semiconductors have an operating limit around 30 to 200 MHz but the higher cellular signal can slightly alter characteristics. A constant 900GHz signal would do nothing but a modulated one can produce the familiar buzz.