It would be interesting to hear anecdotes about whether FBI agents were being issued or were finding it worth purchasing their own notebooks, cell phones, for use in the field back then!
Anecdotes about what we thought was affordable or common place in our neighborhoods isn't very relevant to whether the tech was available for enterprises and workers who needed it.
With no insider knowledge, I can only guess whether a federal agency like the FBI was aggressive with such options or lethargic and stuck in their legacy methods. Likewise, the writers and show producers may have made choices based on what they thought the audience would relate to rather than what was actually possible or in use. Or maybe they didn't have any insider knowledge either..?
However, the term "road warrior" was jargon for a category of business travelers in PC advertising by the late 1980s. There were various portable computers back then, and "notebooks" became idiomatic in the early 90s. PowerBooks and ThinkPads were already around when this show launched, and being used by companies and individuals who saw the value. It's hard for me to imagine that a Hollywood writer wouldn't know about these things if they did any background research at all.
People had modems and various forms of dial-up interface with larger enterprises. You likely dialed a modem bank specific to your employer to access some kind of mainframe app or terminal server within the enterprise. But the transition to things like SLIP and PPP was also happening at this time in some enterprises. And CompuServe and Prodigy were more retail focused. You could imagine agents using something like this in the field much like people today use unofficial social media and personal phones. It's hard to prevent it...
The first 2G digital cellular networks were rolling out in the US around the same time this show launched. But, yeah, coverage was not as universal as it is now.