So I looked into this and found a case in Fort Worth where a 'Cell Phone Tracker' was purchased and it looks like it is marketed and produced by Harris Corporation.[1]
I found their product list if you want to dig through it. [2]
Hmm so I'm guessing basically it's a software-defined radio that can predict the frequency hopping algorithms in phones to distinguish an individual handset's communications. Someone showed something like that at some hacker conference in the last few years, but that was reverse engineered. I'm guessing these guys have access to restricted knowledge from the networks/manufacturers.
The actual triangulation of the position once you can do that is pretty trivial I'd imagine, perhaps with some algorithms for compensating for physical obstructions between you and the target.
I found their product list if you want to dig through it. [2]
[1] http://www.wfaa.com/news/local/Fort-Worth-buys-cell-phone-tr... [2] http://publicintelligence.net/harris-corporation-amberjack-s...