A telephony communication setup request sent from a telephony device to an element of an IP telephony system includes a first encrypted code that is generated using one or more data items that are specific to the telephony device. The element of the IP telephony system receiving the setup request obtains the same data items locally and creates a second encrypted code. If the second code matches the first encrypted code, the telephony device and/or the setup request are authenticated, and the element of the IP telephony system proceeds to setup the requested telephony communication.