1. A method of authenticating a user for a transaction, the method comprising: receiving, at a server computer, a communication indicative of the communication device associated with the user entering a location within a virtual perimeter; in response to receiving the communication and prior to receiving a voice segment from the user, retrieving, via the server computer, a reference for accessing a voice model associated with the user, wherein the voice model is stored in a database, wherein the reference is a pointer to a storage address within the database; using, at the server computer, the reference to access the voice model stored in the database; comparing, at the server computer, the received voice segment to the voice model; determining, at the server computer, whether the user is authenticated for the transaction based at least in part on comparing the received voice segment to the voice model; and transmitting, via the server computer and to a merchant computer, a result of the determining step.