PDA message mechanics: sender code irrelevant?

[The Grim Sleeper]

You cannot forge the sender on wireless packets.

I've tried using to use a stationary console/terminal to run SigCatcher, but I don't know how to make a normal non-wireless message, so I got stumped.
Do you know of any wired transmissions that could be easily created for testing purposes?

If a wireless network card is available in a terminal, can that terminal be used to send PDA messages? And will the sender then default to the used terminal, even tough it is not a PDA-compatible device?