There's a startup in Palo Alto that uses phone signals to track consumers and generate analytics. Perhaps their technology is being used. http://euclidelements.com/
Interesting. Euclid only works with smartphones, in that it appears to simply sniff MAC addresses, and triangulate them with off-the-shelf wi-fi equipment.
I'm guessing the mall tracking systems are using something on the GSM and CDMA spectra, and are sniffing UDIDs?