Oh, that is interesting. There was a UK-based company doing the same thing (http://www.theregister.co.uk/2008/05/20/tracking_phones/) but using the TMSIs of GSM phones.

Seems they are still around as: http://www.pathintelligence.com/

They were using USRP 1s (universal software radio peripheral, from Ettus Research) at the time, although they might have switched hardware platforms by now.