Well, yeah... you can drive around with a modem and possibly find them - at least some of them. Though the "right" modems are kind of tough to find these days, it seems - and there's more "noise" up there than you might think, making the "fun" even greater.

And, like I thought I had indicated... even the "real" databases (like from the providers) aren't complete/accurate. The one I have is pretty good, but it still sucks... it would be great if it were a bit better / more accurate.