Systems and methods are provided for allowing a mobile device user's location and or identity to be determined. According to one aspect of the disclosure, a method of creating a database comprises providing a first wireless router at a point of sale where a credit card is used in a transaction by a credit card holder, obtaining an identity of the credit card holder during the credit card transaction, establishing a wireless link between the first router and a mobile device carried by the credit card holder, obtaining a Media Access Control (MAC) address associated with the credit card holder's mobile device over the wireless link, correlating the identity of the credit card holder with the MAC address of the credit card holder, and storing the correlated identity and MAC address on a server. In some embodiments, a cellular identifier is obtained rather than a MAC address.