800MHZ digital phones/cellular phones could be listened to on 800mhz scanners (I have one, when we lived in our apartment it was interesting, learned more spanish as if i needed to).

It is not (as far as I know) possible (or if it is, easy) to eavesdrop on a digital phone as they use much stronger frequencies and some use differant security measures in order to not allow it (such as changing the frequency every 5 seconds).

I think what they claimed to have is a crock of shit; you can however monitor a landline phone by placing a micro recorder in the TNI box when it's hooked up to the line (note that it'll only record up to the length of what the tape permits). Also note that the type of microcasette recorder you will want is voice activated so that it'll only record when an active connection on the line is presant.
Donate to UGN Security here.
UGN Security, Back of the Web, Elite Web Gamers & VNC Web Design Owner